[CS] Remove CentralSurfaces#isPulsing.

Have NotificationShadeWindowViewController ask DozeServiceHost directly
for the pulsing status.

Bug: 277764509
Test: verified via logging that the shade gets pulsing=true when
receiving notif on AOD, false otherwise
Test: verified you can open the shade while pulsing
Test: atest NotificationShadeWindowViewControllerTest

Change-Id: I41f6d0abfbcb5d817e52920565493a727d4c2627