No, and we're very hesitant to ever develop it, because we've seen too many cases of people breaking into other people's accounts and destroying the contents, either to be malicious or because they want to claim the account for their own, to be comfortable in adding it without an extreme number of safeguards. If there isn't a way to mass-delete posts, an intruder at least has to delete posts one by one, which increases the chance that the account owner will notice something's wrong and be able to reclaim the account before the entire account can be wiped out.