BURs: don't update OP when approving BUR.

When approving or rejecting a BUR, don't edit the OP forum post to add
an EDIT: line stating the request has been approved. Instead just let
the embedded BUR state who it was approved by, and post a reply saying
that the request has been approved.

app/models/bulk_update_request.rb

@@ -60,14 +60,7 @@ class BulkUpdateRequest < ApplicationRecord
 
   module ApprovalMethods
     def forum_updater
-      @forum_updater ||= begin
-        post = if forum_topic
-          forum_post || forum_topic.forum_posts.first
-        else
-          nil
-        end
-        ForumUpdater.new(forum_topic, forum_post: post)
-      end
+      @forum_updater ||= ForumUpdater.new(forum_topic)
     end
 
     def approve!(approver)