Remove arguments from grouped_options_refs

Must have been left over from a previous revision, but the argument
wasn't used anywhere in the method.

app/helpers/application_helper.rb

@@ -89,7 +89,7 @@ module ApplicationHelper
     "Never"
   end
 
-  def grouped_options_refs(destination = :tree)
+  def grouped_options_refs
     repository = @project.repository
 
     options = [