re: Mature whitetail with one side of antlers "deformed", what would you do?

If that is the only two pics I had of him I would wait and try to get better pics this coming season. If he grows another set just like this and you have pics of this before the fighting begins then shoot him with a quickness. Keep these pics and compare to next year and you may find that you have a wall hanger on your hands because you waited and didnt kill him.