Sparky brittle things that rust. I'd hit em with a hand sledge to loosen them and probably yank em out with channel locks. Maybe try a little recking-bar/nail-puller if you have one. Be carefull of your eyes around those things, flying metal and concrete can ouch.

Often these are hardened, difficult to cut. But they break if hammered from the side. The nail usually still projects somewhat. Grinding them off is perhaps neatest, but does leave the stub in the wall.

As mentioned above, make sure that you wear eye protection. They are hardened steel and snap off and fly when you hit them. I once had a tiny piece of one pierce an artery in my arm.

Drive them sideways parallel to the width. A few taps on one side, then a few on the other.
This usually loosens them enough to put a pair of vide grips on them and use a wonder bar to pry against the vice grips to pull them out.