In iOS11, tap on the movie. You'll see a checkmark icon with Downloaded to the right of the checkmark. Click on the word Downloaded and a pop up window will appear asking if you want to remove. I've attached a screenshot.
Note: if you're still in iOS10 the word Downloaded will be in a blue bubble.
Just an FYI, you'll want to quit and relaunch the TV app after you delete to confirm the movie/tv show was deleted.
I tested this on my iPad and iPhone. Hope it helps.