Hi Robert,
Good question — I think the best way to go about clearing out a large number of posts would be the Bulk Delete plugin. The Events Calendar (and Community Events) does not include a bulk delete option outside of what WordPress offers by default, so this would be the next best way.
Sadly, setting posts to auto-expire is also not a support feature. However, I have used this plugin before and it is a nice way to add an expiration date to a post, which will then pull it off the site.
Will these work for you? Please let me know. 🙂
Cheers!
Geoff