Allow sub-comments to be deleted

[Captain-Quack]

(this is a standalone idea from this list)
There have been a lot of reasons I've wanted to do this, whether it be because what was said isn't relevant, or slow wifi made a comment lag and send twice. It could work like Reddit, where the message is replaced with "this comment has been deleted."

If need be, the comment could still be visible to existing users in the discussion, to maintain any context.