Delete an assistant, or take a published copy down by deleting it.

Every row the delete touches is pushed to its /users/ws followers:

• the addressed row, as a delete;
• the copies that go with an assistant, also as deletes — Postgres cascades them away, and nothing else would tell their followers;
• the assistant behind a copy, as an update — deleting a copy is an unpublish, so its posted/pending ids have just changed and a follower still holding the old ones would keep offering a page that is gone.