You can do this to save running the code.
library/XenForo/Model/Session.php
line 55
PHP:
public function getSessionActivityQuickList(array $viewingUser, array $conditions = array(), array $forceInclude = null)
{
// start hack
return;
// end hack
$fetchOptions = array(
'join' => self::FETCH_USER,
'order' => 'username'
);
It's possible to create an add-on to do the above so you won't have to edit the core code every time you upgrade.