Currently, you can hide a show from you calendar or progress page. Hiding from watched progress also hides it from your dashboard on deck. Hiding in those 2 places should work for most users.
This topic proposes a “dropped” status for a show. This would hide from the 3 sections mentioned above + add a “dropped” indicator in places such as the show summary page.Jack commented
I was able to get things off my progress by searching for the show, clicking the "Watched History" purple check mark, then selecting "Remove All".