Series do have a delete page (series/MBID/delete) that works, and enters edits, but is unlinked. This seems unintentional, given that no checking is made at all to whether the series is indeed empty enough to delete (sub can_delete { 1 }) and yet the sub delete { } block specifically says in a comment "No deleting relationship-related stuff because it should probably fail if it's trying to do that". We should get rid, and just let the cleanup tool do its job.