DAR-958 Removed class for grouped recent changes.

These blocks are collapsed by JavaScript in this file: [/resources/jquery/jquery.makeCollapsible.js](https://github.com/Wikia/app/blob/dev/resources/jquery/jquery.makeCollapsible.js)

This change will make our custom stuff match how it is in core: [/includes/ChangesList.php](https://github.com/Wikia/app/blob/dev/includes/ChangesList.php)