'Fraid it isn't, least not as far as I can see. I tried to delete them for my euro superleagues database, but I'm pretty sure the only way to do that now is to assign them to a country you aren't going to play with!
How do you go about creating a new international competition? I'm trying to make a new Nation in NA but don't want to take out one of the better countries that get berths to the Concacaf Champions League.