You can use a centre punch and a hammer to remove these screws.
On the head of the countersunk screw aim the centre punch at a 45 degree angle to the surface, if the head were a dart board place the punch on a double and direct in the direction that would twist the screw in a anticlockwise motion. Give it a good strike and they usually crack off. You can then use the screwdriver to unscrew them. File off the burr the punch has left and reuse.
On the head of the countersunk screw aim the centre punch at a 45 degree angle to the surface, if the head were a dart board place the punch on a double and direct in the direction that would twist the screw in a anticlockwise motion. Give it a good strike and they usually crack off. You can then use the screwdriver to unscrew them. File off the burr the punch has left and reuse.