Generally it's frowned upon to delete a thread if anyone else has posted there but yourself, as I understand it. Especially if it's a story and another person has been writing in it too. Removing your own posts out of a story is also frowned upon because it screws up the story overall.
However, if I created a thread and the only one to post in it was me, I would remove it myself by using the delete button. It's not interfering with anybody else in that situation, and it's not reducing anyone else's post count to do so if the only posts there are your own.
You might want to check with a mod though rather than accepting my advice, because it may not be the official approach.