Remove isPromotedOngoing helper method and debug promoted flag.

Now that the status bar chips don't have a separate flag and we don't
need the debug_live_updates flag, we don't need this helper method at
all.

Bug: 364653005
Bug: 404838239
Test: compiles
Flag: android.app.ui_rich_ongoing
Change-Id: I7a9846b253bf02b832766d57250cd05c83567491