Simplify error in validate_file_to_edit().

props MattyRob for initial patch.
fixes #25924.

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Remove theme support for 'menus' in unregister_nav_menu() when there are no more menus.

props kovshenin.
fixes #26900.

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Use filtered per_page value in WP_Plugin_Install_List_Table and WP_Theme_Install_List_Table.

props brasofilo.
fixes #25675.
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Convert docs for `wp_nav_menu()` arguments to a hash notation.

Fixes #27163.

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Fix reversed return logic in the `wp_nav_menu()` phpdoc.

See #27163.

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