I removed it from the functions qa_html_convert_urls and qa_url_to_html_link - lines 823 and 839 in qa-app-format.php, and it worked for me.
But if that is not working, there are also a couple instances inside qa-htmLawed.php that may be being added. You probably need to remove line 527 and the instances of "nofollow" at the end of lines 515 and 518.