controllers: refactor only param includes.

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

app/controllers/user_feedbacks_controller.rb

@@ -19,7 +19,9 @@ class UserFeedbacksController < ApplicationController
   end
 
   def index
-    @user_feedbacks = UserFeedback.paginated_search(params, count_pages: true).includes(model_includes(params))
+    @user_feedbacks = UserFeedback.paginated_search(params, count_pages: true)
+    @user_feedbacks = @user_feedbacks.includes(:user, :creator) if request.format.html?
+
     respond_with(@user_feedbacks)
   end
 
@@ -37,14 +39,6 @@ class UserFeedbacksController < ApplicationController
 
   private
 
-  def default_includes(params)
-    if ["json", "xml"].include?(params[:format])
-      []
-    else
-      [:user, :creator]
-    end
-  end
-
   def check_privilege(user_feedback)
     raise User::PrivilegeError unless user_feedback.editable_by?(CurrentUser.user)
   end