In `WP_Media_List_Table`, remove dead code:

* In `->prepare_items()`, importing `$wpdb` is unnecessary.
* In `->get_columns()`, `$taxonomies` is set twice before it is used.
* In `->display_rows()`, `$taxonomy_object` is set and never used.

See #27882.



git-svn-id: https://develop.svn.wordpress.org/trunk@28293 602fd350-edb4-49c9-b593-d223f7449a82
Custom Header: Fix logic when a theme doesn't set `default-text-color`.

fixes #28042.

git-svn-id: https://develop.svn.wordpress.org/trunk@28294 602fd350-edb4-49c9-b593-d223f7449a82
In `WP_MS_Users_List_Table::get_views()`, remove dead code:

* `$wp_roles` doesn't need to be imported.
* `$current_role` is set and never used.

See #27882.



git-svn-id: https://develop.svn.wordpress.org/trunk@28295 602fd350-edb4-49c9-b593-d223f7449a82