MAINTAINERS: N900: Remove isp1704_charger.h record

Update MAINTAINERS to reflect that isp1704_charger.h file was removed.

Cc: Pavel Machek <pavel@ucw.cz>
Cc: linux-pm@vger.kernel.org
Fixes: f5d782d4 ("power: supply: isp1704: switch to gpiod API")
Signed-off-by: Denis Efremov <efremov@linux.com>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>