Follow-up from "Use FastDestroy for deleting uploads"

Once we remove fast_destroy_uploads, we can simplify destroy callbacks in WithUploads concern - we can then use has_many :file_uploads ... dependent: :delete_all

The following discussion from !20977 (merged) should be addressed:

• @ayufan started a discussion: (+2 comments)

  The delete_uploads is not executed, as remove_file_uploads is not executed, as fast_destroy_enabled? is true, and before_destroy :remove_file_uploads, unless: :fast_destroy_enabled? callback will not be executed.

  So technically, it should be destroy_file_uploads :)