[flexi] Remove reliance on ScrimStartable/ScrimController

When the scene container flag is enabled:
- DozeScrimController immediately starts
the pulse and schedules the pulseOut instead of relying
on callbacks from ScrimController
- ScrimController should not be used at all

Fixes: 433477971
Flag: com.android.systemui.scene_container
Test: Builds, observe screen on/off scrims look similar
to non-flexi
Test: notification pulse times out
Test: screen-off udfps failure (pulsing state) times out
Test: atest SystemUITests
Test: atest DozeScrimControllerTest

Change-Id: I637297c3e144b69ad5bb7930f4c7d5e82190b154