To delete all the comments that have _not_ been approved yet can be deleted via:
delete from wp_comments where comment_approved=0;
Your table name can be different so wp_comments can be your defined prefix_comments.
*) If you have non-spam comments that need approval they will also be deleted so watch out.
I just went to the DB and deleted all comments needing moderation with a SQL query. If you’re running bleeding edge I guess the bug has not been adressed yet 🙁
Nope but this is an interesting idea. I’ll have to think about it, thx.