Yes, I think this is a bug. This function is no longer used by the core but was included for backwards compatibility, so presumably some plugin is still access it. You can fix it as follows:
return qa_limits_calc_remaining($action, $dblimits['user'], $dblimits['ip']);
... to ...
return qa_limits_calc_remaining($action, @$dblimits['user'], @$dblimits['ip']);