API: don't expose 'updated_at' for notes

doc/api/notes.md

@@ -20,8 +20,7 @@ GET /projects/:id/notes
       "blocked": false,
       "created_at": "2012-05-23T08:00:58Z"
     },
-    "updated_at":"2012-11-27T19:16:44Z",
-    "created_at":"2012-11-27T19:16:44Z"
+    "created_at": "2012-11-27T19:16:44Z"
   }
 ]
 ```

lib/api/entities.rb

@@ -73,7 +73,7 @@ module Gitlab
       expose :id
       expose :note, as: :body
       expose :author, using: Entities::UserBasic
-      expose :updated_at, :created_at
+      expose :created_at
     end
 
     class MRNote < Grape::Entity