Just go to your
Watchlist ->
Edit watchlist -> Check which posts you want to unfollow -> Click in the "remove checked" button at the bottom of the page.
Or you can also do it manually by going to each post and clicking the "unwatch" button at the top-right corner of the thread.
Then, click "mark all messages as read" at the "
Show new replies to your posts" page to clear the list.
Edit: I actually need to confirm if the "Watching" function has anything to do with the "Show new replies to your posts" page.