Fix remove animation running for HUN already seen in shade

Fixes: 277936467
Test: send HUN, open shade, close shade, send second HUN
      => observe no removal animation for first HUN when it times out
Flag: com.android.systemui.notification_avalanche_throttle_hun
Change-Id: I077c2f95c5aaea9a6e529869c3c5e5e1fbbf02e6