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

src/com/android/settings/homepage/SettingsHomepageActivity.java

@@ -46,11 +46,7 @@ public class SettingsHomepageActivity extends FragmentActivity {
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-
         setContentView(R.layout.settings_homepage_container);
-        final View root = findViewById(R.id.settings_homepage_container);
-        root.setSystemUiVisibility(
-                View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_LAYOUT_STABLE);
 
         final View appBar = findViewById(R.id.app_bar_container);
         appBar.setMinimumHeight(getSearchBoxHeight());