How can I remove a cable from a junction box?

I have a ceiling junction box in my garage that has four armored cables coming into it. I want to remove one of the cables as I'm not using it. I don't have access to the back side of the box, because the ceiling is finished (metal lath and plaster).

I'm thinking I could remove this a few different ways:

1. twist the wires together, wire nut, and leave in the box
2. cut the exposed copper, and electrical tape the ends
3. cut the wires back to the cable clamps