BURs: remove old single alias/implication pruning code.

* Rename TagChangeRequestPruner to BulkUpdateRequestPruner.
* Remove old code for pruning individual alias / implication requests.

app/logical/bulk_update_request_pruner.rb

@@ -0,0 +1,27 @@
+module BulkUpdateRequestPruner
+  module_function
+
+  def warn_old
+    BulkUpdateRequest.old.pending.find_each do |bulk_update_request|
+      if bulk_update_request.forum_topic
+        body = "This bulk update request is pending automatic rejection in 5 days."
+        unless bulk_update_request.forum_topic.posts.where(creator_id: User.system.id, body: body).exists?
+          bulk_update_request.forum_updater.update(body)
+        end
+      end
+    end
+  end
+
+  def reject_expired
+    BulkUpdateRequest.expired.pending.find_each do |bulk_update_request|
+      ApplicationRecord.transaction do
+        if bulk_update_request.forum_topic
+          body = "This bulk update request has been rejected because it was not approved within 60 days."
+          bulk_update_request.forum_updater.update(body)
+        end
+
+        bulk_update_request.reject!(User.system)
+      end
+    end
+  end
+end