It was hard but I figured out how to delete. I'm on Deluxe Desktop, downloaded from online. I'm on a Mac.
Get into the view with the list of forms on the side of the screen. (Not in Easy Step mode).
The form I cared about didn't show up in the lefthand list. So I clicked "Open Form," and a search box appeared. Select "California" from the dropdown, otherwise it won't appear. Search for the form number. (Again, won't appear if I didn't select "California" first, which is terrible.)
The form will open.
Then, go to the menu bar at the top of my Mac (not within Turbotax). Click "Forms." Click "Remove Form."