You can comment out the other two pages as follows:
qa-include/pages/updates.php
line 88
$qa_content['navigation']['sub']=array(
//'all' => array(
//'label' => qa_lang_html('misc/nav_all_my_updates'),
//'url' => qa_path_html('updates'),
//'selected' => $forfavorites && $forcontent,
//),
'favorites' => array(
'label' => qa_lang_html('misc/nav_my_favorites'),
'url' => qa_path_html('updates', array('show' => 'favorites')),
'selected' => $forfavorites && !$forcontent,
),
//'myposts' => array(
//'label' => qa_lang_html('misc/nav_my_content'),
//'url' => qa_path_html('updates', array('show' => 'content')),
//'selected' => $forcontent && !$forfavorites,
//),
);