Idk if you want to remove the email notification option altogether, but I did this way:
You can do it (messy way) by modifying the core files:
1) remove in css ----> .qa-form-tall-checkbox {display: none !important}.... Although I noticed this messes up other check boxes like the "save silently to hide that this was edited" block.
2) in /qa-include/lang/qa-lang-question.php ----> remove all the "email if...blah blah blah" wording but leave the quotes