DELETE * FROM qa_posts
You could run that SQL query eg in phpmyadmin, replace "qa" with whatever your table prefix is. (Make sure you delete from the right table!) Then you can run all the scripts in Admin>Stats to clear up everything.
Also just to ask, what exactly are you "cloning"? I mean, you can just set up a new Q2A from scratch and copy your themes/plugins over. What else do you need to copy?