Just get a pair of vice grips, set them at the right pressure, and pull each nail out by “rolling” it.
You are never going to cut them with any type of wire cutters - these are case-hardened steel (to penetrate concrete, capiche?).
Grinding them would work, but it seems a bit obsessive to me.
See my post a few above. Large Channellocks should quickly work without the trouble of using Vice Grips.
BTW, I just realized that I threw out “channel locks” like @beowulff threw out “vice grips”. They are the Kleenex of the slip joint and locking pliers world.