Use throttle flag for group hun animation fix

Use the avalanche throttle hun flag for the group hun animation fix.
Because this bugfix improves the animation quality when the throttle
hun is enabled.

Fix: 357121423
Flag: com.android.systemui.notification_avalanche_throttle_hun
Test: HeadsUpCoordinatorTest
Change-Id: I0a615b1720c72f009cbee79efbcaf171a1ed6c36