Inline notif pipeline flag into new pipeline code

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: I8e1b0eb0a6cd7b43e1ff3cb5292d187f46810202
Merged-In: I8e1b0eb0a6cd7b43e1ff3cb5292d187f46810202