power: supply: ds2760: Remove unused ds2760_battery_set_charged

power: supply: ds2760: Remove unused ds2760_battery_set_charged

With power_supply_set_battery_charged() deleted in the previous
patch, there's no one left to call the set_charged method.
The only implemented is in ds2760, unwire it and delete the
associated functions and data.

(Arguably it might be time to delete ds2760 since I don't
think there are any users left)

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20250307230225.128775-3-linux@treblig.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>