Remove unused service method.

app/models/service.rb

@@ -92,8 +92,4 @@ class Service < ActiveRecord::Base
   def issue_tracker?
     self.category == :issue_tracker
   end
-
-  def self.issue_tracker_service_list
-    Service.select(&:issue_tracker?).map{ |s| s.to_param }
-  end
 end