How do I unsubscribe from a thread?

Are you referring to bookmarking?

If you bookmarked using the actions bar on the right, then you can remove yourself the same way using the actions bar.
((On the left for mobile users))

Also- people quoting you/liking your post is more of a manual way of keeping you alerted. People must really love your words! LOL (I'm joking of course)

As of this moment, the participation tab does not seem to have a delete function. ^^

Bare with me- My connection from home is spiking up...
((My brother is probably playing on all consoles online at the same time... r.i.p))

If you go to profile - 

Edit Profile > Notifications

You should be able to check and un-check settings that you do not want to pop up on your notifications!

Yeah, I mean the 'Participated' notification button. Most of the things that pop up in there I do want to be notified of, but some things (like the counting thread) I don't want to be notified of, especially when I think it's something important that's been updated. So I guess I'll just leave them be until they disappear.

Thanks for your replies! 

Yeah that's what I do. But I'll try to avoid it now I know it'll be readded to the list