Solved. Please delete.

[kh99]

OK, to remove the prune button you could edit the file includes/xml/cpnav_vbulletin.xml and take out the part for that button, or you could make a plugin at hook admin_index_navigation with code:

unset($navigation[80]['Threads & Posts']['options'][10]);

That obviously depends on exactly the way the xml file is, so it would probably be better (if you go the plugin route) to search all the items looking for the prune button.