What to do with ground wire in light fixture?
If it's a metal box with EMT, then the box is probably grounded and you could attach the ground from the light to a 10-32 ground screw into the box. If it old style NM cable with no ground, then just tuck the ground wire into the box away from the other wires. You can fold it and tape with electrical tape if it helps you sleep at night. There is no way then to ground your fixture.