I just had this bug, but with the Stray Dog. Happily a fellow forum member found the solution.
If you want to get rid of your follower ANIMAL, then write into the console: "set playeranimalcount to 0"
If you want to get rid of a normal FOLLOWER, then write this into the console: "set playerfollowercount to 0"
Well it seems you just forgot about the quest... Anyway, these commands might help people with similar problems