Index: src/js/_enqueues/wp/customize/nav-menus.js
===================================================================
--- src/js/_enqueues/wp/customize/nav-menus.js	(revision 46636)
+++ src/js/_enqueues/wp/customize/nav-menus.js	(working copy)
@@ -3027,83 +3027,6 @@
 		}
 	} );
 
-	api.Menus.NewMenuControl = api.Control.extend(/** @lends wp.customize.Menus.NewMenuControl.prototype */{
-
-		/**
-		 * wp.customize.Menus.NewMenuControl
-		 *
-		 * Customizer control for creating new menus and handling deletion of existing menus.
-		 * Note that 'new_menu' must match the WP_Customize_New_Menu_Control::$type.
-		 *
-		 * @constructs wp.customize.Menus.NewMenuControl
-		 * @augments   wp.customize.Control
-		 *
-		 * @deprecated 4.9.0 This class is no longer used due to new menu creation UX.
-		 */
-		initialize: function() {
-			if ( 'undefined' !== typeof console && console.warn ) {
-				console.warn( '[DEPRECATED] wp.customize.NewMenuControl will be removed. Please use wp.customize.Menus.createNavMenu() instead.' );
-			}
-			api.Control.prototype.initialize.apply( this, arguments );
-		},
-
-		/**
-		 * Set up the control.
-		 *
-		 * @deprecated 4.9.0
-		 */
-		ready: function() {
-			this._bindHandlers();
-		},
-
-		_bindHandlers: function() {
-			var self = this,
-				name = $( '#customize-control-new_menu_name input' ),
-				submit = $( '#create-new-menu-submit' );
-			name.on( 'keydown', function( event ) {
-				if ( 13 === event.which ) { // Enter.
-					self.submit();
-				}
-			} );
-			submit.on( 'click', function( event ) {
-				self.submit();
-				event.stopPropagation();
-				event.preventDefault();
-			} );
-		},
-
-		/**
-		 * Create the new menu with the name supplied.
-		 *
-		 * @deprecated 4.9.0
-		 */
-		submit: function() {
-
-			var control = this,
-				container = control.container.closest( '.accordion-section-new-menu' ),
-				nameInput = container.find( '.menu-name-field' ).first(),
-				name = nameInput.val(),
-				menuSection;
-
-			if ( ! name ) {
-				nameInput.addClass( 'invalid' );
-				nameInput.focus();
-				return;
-			}
-
-			menuSection = api.Menus.createNavMenu( name );
-
-			// Clear name field.
-			nameInput.val( '' );
-			nameInput.removeClass( 'invalid' );
-
-			wp.a11y.speak( api.Menus.data.l10n.menuAdded );
-
-			// Focus on the new menu section.
-			menuSection.focus();
-		}
-	});
-
 	/**
 	 * Extends wp.customize.controlConstructor with control constructor for
 	 * menu_location, menu_item, nav_menu, and new_menu.
@@ -3113,7 +3036,6 @@
 		nav_menu_item: api.Menus.MenuItemControl,
 		nav_menu: api.Menus.MenuControl,
 		nav_menu_name: api.Menus.MenuNameControl,
-		new_menu: api.Menus.NewMenuControl, // @todo Remove in a future release. See #42364.
 		nav_menu_locations: api.Menus.MenuLocationsControl,
 		nav_menu_auto_add: api.Menus.MenuAutoAddControl
 	});
Index: src/wp-includes/class-wp-customize-manager.php
===================================================================
--- src/wp-includes/class-wp-customize-manager.php	(revision 46636)
+++ src/wp-includes/class-wp-customize-manager.php	(working copy)
@@ -317,7 +317,6 @@
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menu-name-control.php' );
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menu-locations-control.php' );
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menu-auto-add-control.php' );
-		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-new-menu-control.php' ); // @todo Remove in a future release. See #42364.
 
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menus-panel.php' );
 
@@ -325,7 +324,6 @@
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-themes-section.php' );
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-sidebar-section.php' );
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menu-section.php' );
-		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-new-menu-section.php' ); // @todo Remove in a future release. See #42364.
 
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-custom-css-setting.php' );
 		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-filter-setting.php' );
Index: src/wp-includes/class-wp-customize-section.php
===================================================================
--- src/wp-includes/class-wp-customize-section.php	(revision 46636)
+++ src/wp-includes/class-wp-customize-section.php	(working copy)
@@ -383,14 +383,3 @@
 
 /** WP_Customize_Nav_Menu_Section class */
 require_once( ABSPATH . WPINC . '/customize/class-wp-customize-nav-menu-section.php' );
-
-/**
- * WP_Customize_New_Menu_Section class
- *
- * As this file is deprecated, it will trigger a deprecation notice if instantiated. In a subsequent
- * release, the require_once() here will be removed and _deprecated_file() will be called if file is
- * required at all.
- *
- * @deprecated 4.9.0 This file is no longer used due to new menu creation UX.
- */
-require_once( ABSPATH . WPINC . '/customize/class-wp-customize-new-menu-section.php' );
Index: src/wp-includes/customize/class-wp-customize-new-menu-control.php
===================================================================
--- src/wp-includes/customize/class-wp-customize-new-menu-control.php	(revision 46636)
+++ src/wp-includes/customize/class-wp-customize-new-menu-control.php	(working copy)
@@ -8,6 +8,8 @@
  * @deprecated 4.9.0 This file is no longer used as of the menu creation UX introduced in #40104.
  */
 
+_deprecated_file( basename( __FILE__ ), '4.9.0' );
+
 /**
  * Customize control class for new menus.
  *
@@ -30,13 +32,14 @@
 	 * Constructor.
 	 *
 	 * @since 4.9.0
+	 * @deprecated 4.9.0
 	 *
 	 * @param WP_Customize_Manager $manager Manager.
 	 * @param string               $id      ID.
 	 * @param array                $args    Args.
 	 */
 	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
-		_deprecated_file( basename( __FILE__ ), '4.9.0' ); // @todo Move this outside of class, and remove its require_once() from class-wp-customize-control.php. See #42364.
+		_deprecated_function( __METHOD__, '4.9.0' );
 		parent::__construct( $manager, $id, $args );
 	}
 
@@ -44,8 +47,10 @@
 	 * Render the control's content.
 	 *
 	 * @since 4.3.0
+	 * @deprecated 4.9.0
 	 */
 	public function render_content() {
+		_deprecated_function( __METHOD__, '4.9.0' );
 		?>
 		<button type="button" class="button button-primary" id="create-new-menu-submit"><?php _e( 'Create Menu' ); ?></button>
 		<span class="spinner"></span>
Index: src/wp-includes/customize/class-wp-customize-new-menu-section.php
===================================================================
--- src/wp-includes/customize/class-wp-customize-new-menu-section.php	(revision 46636)
+++ src/wp-includes/customize/class-wp-customize-new-menu-section.php	(working copy)
@@ -8,6 +8,8 @@
  * @deprecated 4.9.0 This file is no longer used as of the menu creation UX introduced in #40104.
  */
 
+_deprecated_file( basename( __FILE__ ), '4.9.0' );
+
 /**
  * Customize Menu Section Class
  *
@@ -32,13 +34,14 @@
 	 * Any supplied $args override class property defaults.
 	 *
 	 * @since 4.9.0
+	 * @deprecated 4.9.0
 	 *
 	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
 	 * @param string               $id      An specific ID of the section.
 	 * @param array                $args    Section arguments.
 	 */
 	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
-		_deprecated_file( basename( __FILE__ ), '4.9.0' ); // @todo Move this outside of class, and remove its require_once() from class-wp-customize-section.php. See #42364.
+		_deprecated_function( __METHOD__, '4.9.0' );
 		parent::__construct( $manager, $id, $args );
 	}
 
@@ -46,8 +49,10 @@
 	 * Render the section, and the controls that have been added to it.
 	 *
 	 * @since 4.3.0
+	 * @deprecated 4.9.0
 	 */
 	protected function render() {
+		_deprecated_function( __METHOD__, '4.9.0' );
 		?>
 		<li id="accordion-section-<?php echo esc_attr( $this->id ); ?>" class="accordion-section-new-menu">
 			<button type="button" class="button add-new-menu-item add-menu-toggle" aria-expanded="false">
