I'm searching for that too, you can hide it with css but thats not a nice way.
the other option would be to delete it from the code in the file qa-theme-base.php:
function nav_main_sub()
{
$this->nav('main');
$this->nav('sub');
}
Thats where its produced, but you can't just delete that line, because it will also delete the admin-bar, so we need to get into that nav('sub'); but i dont know how, maybe some experts can help ...