It's nearly impossible to remove them from the wood of the plane. Your best bet is to simply cut them off flush with the wood and cut a new hinge slot next to the old one. More often than not when you try to dig out old CA hinges you'll cause more damage to the wood of the plane. It's not impossilbe to do, but very very difficult to do. IMHO it's just not worth the effort to try and dig out the old hinge.

Ken