Don't bother creating the user index on user_roles as migration 48 will

create one on user+role that will do the same job.

Removing it here is a bit of a hack as it will not get dropped from
existing databases but as it was not given an explicit name it is hard
to write a migration to drop it.

db/migrate/044_create_user_roles.rb

@@ -17,7 +17,6 @@ class CreateUserRoles < ActiveRecord::Migration
     remove_column :users, :administrator
 
     add_foreign_key :user_roles, [:user_id], :users, [:id]
-    add_index :user_roles, [:user_id]
   end
 
   def self.down