[flexiglass] Reset KeyguardFading/GoingAway after transition to Gone

Due to ScrimController being deprecated in flexi, the codepath that reset KeyguardFadingAway/KeyguardGoingAway state was removed and not replaced. This brings it back in ScrimStartable.

Bug: 372746998
Test: manually verified that trying to expand sensitive notifications in locked shade properly brings up bouncer
Test: now passes ExpandSensitiveNotificationOnLockScreen
Flag: com.android.systemui.scene_container
Change-Id: Idd4bcb344332a5daf857304928974758ae4ca245