You (or someone) has already removed the locking. To remove the cup, the proper tool would be a pin spanner like the Park Tool SPA-1. You can improvise, though. You just need something that'll fit in the holes so you can turn the cup counter-clockwise. I've used needlenose pliers in a pinch. Open 'em up, put the tips in two different holes on the cup, and turn. It might not be so easy with all that corrosion, though.