This is a good candidate for an option in a future version. In the meantime you can change it as follows:
Questions: modify this in qa-page-ask.php:
$innotify=true;
... to ...
$innotify=false;
Answers: modify this in qa-page-question.php:
isset($innotify) ? $innotify : true
... to ...
isset($innotify) ? $innotify : false
For comments, it's off by default anyway.