Deprecate/remove custom-fields.js and categories.js

[ocean90]

admin-categories aka wp-admin/js/categories.js is unused since 3.1.

admin-custom-fields aka wp-admin/js/custom-fields.js is unused since 2.5.

[nacin]

Only instances in the plugin directory of either are:

plugins/zelist/admin/link-categories.php:49:wp_enqueue_script('admin-categories');
plugins/zelist-directory/wp-admin/categories.php:128:wp_enqueue_script( 'admin-categories' );

Both of which are straight copies of the link-categories.php and categories.php wp-admin files.

[nacin]

In 23446:

Remove unused admin-categories and admin-custom-fields JavaScript files. props ocean90. fixes #23486.

[pat@…]

These files have been left in the zip package as 0-byte files which results in a copy error when unzipping the package using PHPs ZipArchive library. They should be removed from the zip archive if they have been deprecated/removed.

[nacin]

In 25013:

Remove zero-byte files that were meant to be deleted in [23446]. see #23486.

[nacin]

In 25014:

Remove zero-byte files that were meant to be deleted in [23446]. see #23486.

Merges [25013] to the 3.6 branch.

[duck_]

[25013] missed out adding the files to $_old_files in trunk, see 23486.old-files.diff​.

[duck_]

In 25019:

Add javascript files deleted in [25013] to $_old_files. See #23486.