Delete one comment from a question of an answer request

Permanently removes a single comment from the thread on one question of one answer request — the write behind the delete action in the comment popover on the answer and review pages. Only the comment author may delete it; anyone else gets 403 cannot_delete_question_comment, including other people at the same company. The comment must be filed against the addressed question and request, otherwise 404 question_comment_not_found — the same code an unknown comment answers, so the endpoint never confirms a comment the caller cannot address exists elsewhere. The delete is permanent: the row is removed, not flagged. Answers 204 with an empty body.