To me it looks like a worn out allen head. I don't see a seam for a roll pin. My Stepdad taught me a trick on things like this. Use a tool steel pin set and start gently on the side tapping the set and frequently spray with a rust remover. It takes patience but it has never let me down. I have removed busted off rusty bolts and the like. The constant light tapping simulates an impact wrench. It will work even if that is a roll pin.