api: remove available_includes dependent on current user.

This is to avoid specifying permissions in multiple disjoint places and
because most API users shouldn't need these fields.

app/models/forum_topic.rb

@@ -179,8 +179,6 @@ class ForumTopic < ApplicationRecord
   end
 
   def self.available_includes
-    includes_array = [:creator, :updater, :original_post]
-    includes_array << :moderation_reports if CurrentUser.is_moderator?
-    includes_array
+    [:creator, :updater, :original_post]
   end
 end