I only glanced at the code...

You'll need to open the adminpasswd.db or passwd.db file, find the line with the user and delete them. Here's one node, How do I delete/modify one line from test file ?, and I'm sure you can find others on the site.

Frankly I'd follow the advice of the others on this thread and stuff it into a real database (MySQL or PostgreSQL are both good). Doing that will make your life a lot easier in the long run.