dt-bindings: power: supply: Drop redundant monitored-battery ref

Bindings reference the common power supply schema, which already defines
the type (ref) for "monitored-battery" property.  Drop the redundant ref
from individual device schemas along with obvious description also
duplicating what is in power-supply.yaml.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250604-dt-bindings-psy-monitored-battery-v1-6-7f755ff75218@linaro.org


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