power: supply: Remove unused set_charged method

The previous patches in this series removed the only caller
and only setter of this method.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20250307230225.128775-4-linux@treblig.org


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>