Refactor Date & Time Settings

- Rid off AbstractPreferenceController

Test: robotest
Bug: 235445309
Change-Id: I61118a0ff580231973509c06e84e7088dba897f5

tests/robotests/src/com/android/settings/datetime/TimeZonePreferenceControllerTest.java

@@ -66,15 +66,10 @@ public class TimeZonePreferenceControllerTest {
 
         mPreference = new RestrictedPreference(mContext);
 
-        mController = spy(new TimeZonePreferenceController(mContext));
+        mController = spy(new TimeZonePreferenceController(mContext, "test_key"));
         doReturn("test timezone").when(mController).getTimeZoneOffsetAndName();
     }
 
-    @Test
-    public void isAlwaysAvailable() {
-        assertThat(mController.isAvailable()).isTrue();
-    }
-
     @Test
     public void updateState_suggestManualNotAllowed_shouldDisablePref() {
         // Make sure not disabled by admin.