[Provider Model] Internal cleanup - remove Provider Model flag and deprecated legacy UI part.4 am: ad79a1819f am: c4d1fc4fd2

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/16475177

Change-Id: I759453090ac063dc4d8c79c1a18bcfb2cd861871