In `wp_delete_attachment()`: account for orphan sizes by looping over the sizes stored in metadata, instead of relying on the current sizes stored in `$_wp_additional_image_sizes`.

Props JoshuaAbenazer, desrosj, markoheijnen.
Fixes #24518.


git-svn-id: https://develop.svn.wordpress.org/trunk@29816 602fd350-edb4-49c9-b593-d223f7449a82