controllers: refactor only param includes.

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

app/controllers/forum_posts_controller.rb

@@ -24,7 +24,9 @@ class ForumPostsController < ApplicationController
   end
 
   def index
-    @forum_posts = ForumPost.paginated_search(params).includes(model_includes(params))
+    @forum_posts = ForumPost.paginated_search(params)
+    @forum_posts = @forum_posts.includes(:topic, :creator) if request.format.html?
+
     respond_with(@forum_posts)
   end
 
@@ -68,14 +70,6 @@ class ForumPostsController < ApplicationController
 
   private
 
-  def default_includes(params)
-    if ["json", "xml"].include?(params[:format])
-      []
-    else
-      [:topic, :creator]
-    end
-  end
-
   def load_post
     @forum_post = ForumPost.find(params[:id])
     @forum_topic = @forum_post.topic