How do I remove shows from TV Shows list?

In iTunes, the TV Shows tab lists several shows that I have purchased and watched. I have successfully deleted the already-watched content from my computer and iOS devices and they no longer appear under TV Shows in my iTunes library. I would now like to remove them from the TV Shows | Shows list (under Sync TV Shows). I have tried selecting each and tapping Delete and selecting each and right-clicking, but I'm unable to remove them.

How do I clear this list of already-watched shows/seasons?