There is a way to do that... when you go to the ban user page... there is a link at the bottom that does just that. It will even prompt you to ask if you are sure before doing it.
EDIT: Correction- Open up the edit user page...at the bottom it has links to delete user. Use that and it will do what you were asking. It will ask to confirm before it does it.
Dunny
Last edited by Dunny; 05/05/2012 3:25 PM.