There is an option in the CCC iDrive to delete programmable key memory, seems to have disappeared altogether in the CIC system
Hopefully somebody more knowledgeable can chime in with an answer, now I'm curious!
There is a section titled Programmable memory keys
in the owner's manual. It mentions nothing of deleting them however there must be a way to reprogram them to do nothing in particular and, therefore, bring them back to an unprogrammed state.