by Ken Task.
The only thing one could do is to delete tables whose prefix is mdl_.
All the tables related to WP begin with a wp_ prefix. Assuming you left those config items at their defaults. In theory that does work ... one database - two non related apps - using different prefixes.
Since I've never combined apps into one DB, can't tell you how to do that via a 'magic command', but if you have PHPMyadmin, one should be able to see the prefixes clearly and manually remove the appropriate tables / indexes.
Test query using the database:
show tables like "%mdl_%";
or
show tables like "%wp_%";
should list them.
Wish you luck!
'spirit of sharing', Ken