You can stop sending the emails by removing or commenting out this line:
$RecipientEmail = "".((isset($_POST["UserEmail"]))?$_POST["UserEmail"]:"") ."";include("../../../webassist/email/WAUE_users_Registration_1.php");
It will be on the page: webassist/plugins/registration/registration.php (line 127)
and on the page: webassist/plugins/registration/full/registration.php (line 151)
Depending on whether you use the full or short registration form you could update one or the other, or just do both.
If you have trouble with emails not sending, try using this updated set of files: showpost.php?p=97588&postcount=4