thermal: rcar: remove machine_power_off() from rcar_thermal_notify()

Machine/System power-off is run in thermal frame work if
it become critical temperature.
This patch removed pointless machine_power_off()
from thermal_zone_device_ops :: .notify

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>