Always collect animation flows in KeyguardViewMediator

Instead of tying the flows to the keyguard root view, always collect
them in case the root view hasn't been initialized by the time
systemReady runs. In this case, the animations break.

Fixes: 333074624
Flag: NONE
Test: atest KeyguardViewMediatorTest
Change-Id: Icc24e3c1cc65ddd73d5ed20cbcd69010681ae259