Inline notif pipeline flag into NotifController

This change is a no-op; the flag is now enabled-by-default, so all
removed code paths here are effectively dead.

Bug: 200269355
Test: atest SystemUITests
Change-Id: I1aa582cd30b43f5fc9f720b67e37cfa9e6460f5e
Merged-In: I1aa582cd30b43f5fc9f720b67e37cfa9e6460f5e