Remove code that check for dashboard feature.

- remove DashboardFeatureProvider.isEnabled() and all relating code
and tests.

Bug: 35764802
Test: make RunSettingsRoboTests
Change-Id: If7796677abc8904b7436525836d50cdef38e37a4

tests/robotests/src/com/android/settings/dashboard/DashboardSummaryTest.java

@@ -75,7 +75,6 @@ public class DashboardSummaryTest {
     @Test
     public void updateCategoryAndSuggestion_shouldGetCategoryFromFeatureProvider() {
         doReturn(mock(Activity.class)).when(mSummary).getActivity();
-        when(mDashboardFeatureProvider.isEnabled()).thenReturn(true);
         mSummary.updateCategoryAndSuggestion(null);
         verify(mDashboardFeatureProvider).getTilesForCategory(CategoryKey.CATEGORY_HOMEPAGE);
     }