Right now I can find no other way to remove a user than to manually delete them from the wiki database. Here are the steps (warning: there is no undoing this):
- Goto http://hades.mech.northwestern.edu/phpMyAdmin/
- Log into the MySQL server (this username/password is different than the webserver)
- In the left-hand column, click on "user"
- Now click "Browse" from the top of the main frame
- Click the red "X" next to the username you wish to delete.
- Make sure to logout of the phpMyAdmin client or close the browser afterwards.