First off, back up your database. This answer is for Donut v.2.0.2.
A bunch of them are listed in the array found here:
and some others here:
Match them up with the output of the following SQL query (assuming your database prefix is "qa_"):
SELECT title FROM qa_options WHERE title LIKE 'donut_%';
If they match up, then run the following query:
DELETE FROM qa_options WHERE title LIKE 'donut_%';
Otherwise, you’ll need to removed the ones mentioned in the source code one by one.
If you’re going to re-install the plug-in later on, make sure to visit Admin > Plugins page to get its default options set up.