The CSS way: Just hide the HTML.
Edit your theme's CSS file and add this class at the bottom:
.qa-template-questions .qa-nav-sub-list {
display: none;
}
The PHP way: Don't even send the HTML to the client.
Edit your theme's qa-theme.php file and make the doctype function look like this (make any needed additional change):
function doctype(){
qa_html_theme_base::doctype();
if ($this->template === 'questions') {
unset($this->content['navigation']['sub']);
}
}
Let me know if this is what you're looking for.