Deleting your post (and hence the thread) would defeat part of the point of a forum: someone else with the same problem being able to find an existing answer.
You can always post back to the thread "great, that fixed it, thanks" or similar. Those who read the thread will then know that the question is answered. Those who don't bother reading it and post anyway, well it's their business. You could use the "report" option to ask the mods to close each thread, but you could argue that's also wasting their time. And of course it's possible that someone might still post something that would be helpful to someone else. So my advice would be to ignore the thread once you are done and don't worry about what other people choose to do.