If you made something haram to get them then they are haram otherwise, they are halal. In other words, if you are getting them from faucets / Mining or giveaways then It's halal but from Gambling it's Haram.
Now you should know how much you deposited into the wallet and from where exactly . I'm pretty sure the bitcoin addresses of gambling websites are known so It shouldn't be a problem to know where you (gambling website) received them once that's done you should get rid of them. (give them away to someone (making sure they will not return to you in any way) or to a charity or something).