1: Go to the deviation.
2: Scroll down to where the stat for favs and views are, then click on "who?"
3: Select the desired username
4: Copy it, then head to settings
5: Under General, paste the username into the "blocked usernames" list
6: Block, thus removing all of your art from their favorites.
7: Unblock, and now you have removed your art from their favs without having them wonder why they were blocked.