BURs: don't log mod actions for aliases/implications/mass updates.

Don't log mod actions when aliases, implications, or mass updates are
processed.

Originally aliases and implications were logged because they could be
approved outside of a BUR. Mass updates could also be performed by mods
without making a forum request. This is no longer the case.

They were also logged for debugging purposes. This is no longer needed.
This generated a lot of spam in the mod action logs when a large BUR was
approved.

app/jobs/tag_batch_change_job.rb

@@ -7,7 +7,6 @@ class TagBatchChangeJob < ApplicationJob
 
     CurrentUser.scoped(User.system) do
       migrate_posts(normalized_antecedent, normalized_consequent)
-      ModAction.log("processed mass update: #{antecedent} -> #{consequent}", :mass_update)
     end
   end