As far as my knowledge goes there's no such option.Only edit option only is there or there's Report option where, i think you can request the Mods or admins to delete your thread .Gurus can answer it better thou.
You can delete individual posts (though I wouldn't recommend it - it can make following posts in the thread very confusing) but not entire threads. Yes the MODS can delete an entire thread but this is only usually done if the thread contravenes one of the forum rules.
Remember that the forum is a community where we can share both problems and solutions. Although you may feel that your question has been answered and is therefor no longer needed other users are also viewing the thread and will be getting valuable help and support from it. For example if you look at your thread entitled "Poor Editing" it has been viewed 217 times (as of writing this) - I am willing to bet that isn't just you and the responders viewing it 217 times. I suspect that some other users have gained valuable knowledge from your post (so thank you for asking the question ). This is also the reason why you cant delete your thread.