Fix the scrolling problems in homepage

- Remove the deprecated API and parameter usages of setting system ui
  visibility, which make the app bar scrolling behavior abnormal when
  the navigation bar is enabled.
- Remove the duplicate navigationBarColor of the homepage theme since
  Theme.Settings has configured it.
- Remove the unused scroll flags in search bar layout since its parent
  is no longer AppBarLayout.

Test: visual, robotest
Fixes: 178497625
Fixes: 179122861
Change-Id: I91537cff4f3d98e4bc31e6e42d23895df312fbd4