[nikwho]

I would pressure wash as much off as you can, then continue removing remnants with a fairly fine sand paper, maybe start with 320 and carefully sand it down, trying to minimalize how much you cut into original paint, then wet sand increasingly fine to 500 or 600 grit, followed by rubbing compound, then polishing compound, then wax. Hard to get the primer off without cutting into the original paint some. Most likey(but hard telling) the original paint was scuffed prior to application of primer, anyway.

Good luck!
Nik