The same is true for getting blue medals from the chests. All they do is take up room in the pack or the bank and you can not even sell them. At least you can avoid getting a map if you already have one.
You can always save them for when they release new heroes... If they ever do. I wouldn't get rid of them if I were you. If they release new heroes, you'll have them; if they don't you'll eventually stop playing. In either case, you don't really lose.