Fix AoD front scrim being opaque at DOZE_PULSING.

When doze state changed from DOZE to DOZE_PULSING on devices not
supporting doze_brightness_sensor_type sensor, there would be no
sensor events to update the AoD front scrim. And due to the scrim was
set to opaque at DOZE state, most views on the statusbar will be
invisible. This patch change the scrim to transparent again at leaving
DOZE state.

Bug: 148129743
Test: atest DozeScreenBrightnessTest
Change-Id: I2c079d081b04f00a929ae5c4475639685f9f7e69