controllers: refactor only param includes.

Add extra includes needed by the `only` param inside `respond_with`.

app/controllers/moderation_reports_controller.rb

@@ -10,7 +10,9 @@ class ModerationReportsController < ApplicationController
   end
 
   def index
-    @moderation_reports = ModerationReport.paginated_search(params, count_pages: true).includes(model_includes(params))
+    @moderation_reports = ModerationReport.paginated_search(params, count_pages: true)
+    @moderation_reports = @moderation_reports.includes(:creator, :model) if request.format.html?
+
     respond_with(@moderation_reports)
   end
 
@@ -29,14 +31,6 @@ class ModerationReportsController < ApplicationController
 
   private
 
-  def default_includes(params)
-    if ["json", "xml"].include?(params[:format])
-      []
-    else
-      [:creator, :model]
-    end
-  end
-
   def model_type
     params.fetch(:moderation_report, {}).fetch(:model_type)
   end