Hank, I don't mean to be nosey, but how come ya taken it off? If it were mine, I'd get a piece of metal that would fit in the slots, a hammer, and a buddy to hold the rifle. Tap the metal piece in the off direction. Unless it was soldered on it should come off. Hopefully your sight won't come off with it. If it does, you will have to make a drift punch out of alum , brass, or even a dowel rod, and drive it out.
Btw, the flashhider alone is not illegal, unless your state law prohibits. The folding stock & protruding pistol grip handle on a post ban is 2 bad things.