[loader] Fixed Gallery build tag

Regarding [YUI Gallery Deprecation Announcement][1], it needs to removes the script to fetches the Gallery version and fixes the Gallery build tag. The last build tag is `gallery-2014.06.12-21-45`.

Default Gallery build tag within YUI will be `@GALLERY@` without this changes.

[1]: http://www.yuiblog.com/blog/2014/06/16/yui-gallery-deprecation-announcement/