Sometimes it would be useful if one could delete one's own posting in the forum - at least when there is not yet any reply to it. (For cases like inadvertent duplicate postings, posting in the wrong subforum by mistake, or replying in a thread that has received a better answer while the message was composed)
You can always report your message and someone will take care of it for you. I think it's a rights setting that would give you more rights than just deleting your own posts.
You could just edit them, erase the contests, and post a new title that says "Admins please delete" I suppose what would also help in (at least this case) is for the thread author to be able to lock a thread themselves.
I'd prefer hitting the report to moderator button, as I go through the reports first thing when I see a reported thread. I may never find an edited post that asks me to delete it.