[flexiglass] Fix SecureCamera disappearing on Gone

On Flexiglass the secure camera was only checking for the Keyguard
state GONE which got deprecated to evaluate whether it should be
deactivated. This change is adding a check for Scenes.Gone for
Flexiglass and adding a test for that.

Test: KeyguardInteractorTest (with Flexiglass on and off)
Bug: 416717144
Flag: com.android.systemui.scene_container
Change-Id: I2c60d9f4b93fdb848553e8ffd91c0c180bff198f