controllers: refactor only param includes.

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

app/controllers/users_controller.rb

@@ -31,7 +31,9 @@ class UsersController < ApplicationController
       return
     end
 
-    @users = User.paginated_search(params).includes(model_includes(params))
+    @users = User.paginated_search(params)
+    @users = @users.includes(:inviter) if request.format.html?
+
     respond_with(@users)
   end
 
@@ -94,14 +96,6 @@ class UsersController < ApplicationController
 
   private
 
-  def default_includes(params)
-    if ["json", "xml"].include?(params[:format])
-      []
-    else
-      [:inviter]
-    end
-  end
-
   def item_matches_params(user)
     if params[:search][:name_matches]
       User.normalize_name(user.name) == User.normalize_name(params[:search][:name_matches])