How to remove strange looking strike plate
(This isn't its original shape, is it? I'm guessing that it was attached flat to the frame, and you bent it while trying to get it out?)

Maybe it's meant to reinforce the strike plate, to make it harder to kick the door in. I never saw anything like this - but if you can't yank it out, even with pliers, then obviously it's attached to something behind the door trim. I see these options:


Pry off the door trim piece (on the left in the photo) and see what the hell is under there.
Cut off the exposed part of the metal thingy with a Dremel.
Leave it in place, attach the new strike plate on top of it. (If there's enough space between the frame and the door.)