Index: src/wp-includes/class-wp-customize-manager.php
===================================================================
--- src/wp-includes/class-wp-customize-manager.php	(revision 36213)
+++ src/wp-includes/class-wp-customize-manager.php	(working copy)
@@ -1198,6 +1198,13 @@
 	 * @param string $id Panel ID to remove.
 	 */
 	public function remove_panel( $id ) {
+		$core_panels = array(
+			'widgets',
+			'nav_menus',
+		);
+		if ( in_array( $id, $core_panels ) ) {
+			_doing_it_wrong( 'WP_Customize_Manager::remove_panel', sprintf( 'Removing %s with remove_panel will cause PHP warnings. Use the customize_manager_contruct action instead. See %s.', $id, '<a href="https://core.trac.wordpress.org/ticket/33552#comment:8">https://core.trac.wordpress.org/ticket/33552#comment:8</a>' ), '4.5' );
+		}
 		unset( $this->panels[ $id ] );
 	}