Factors out list of lifetime extenders from NotificationEntryManager.

This allows us to remove the dependency from NotificationEntryManager on
AmbientPulseManager, which at this point was just there as a lifetime
extender.

Test: atest SystemUITests, manual
Change-Id: I3c995fb81c9e628368b720d9e3ac582b2dae7a74
2 files changed