Suppress work-profile search terms when no AfW is on device

- Share the same set of pref controller between main UI and search
  in AccountDashboardFragment.
- Update WorkSoundPreferenceController to actually do something for
  updateNonIndexable() method.
- LockscreenDashboardFragment to also suppress "Work notification" header. I
  think we just missed it previously.

Change-Id: Ifa6f9b2077c9810ffff33f240929f418d4a8a5aa
Fixes: 62167659
Test: robotests