Use searchable="false" to suppress nonIndexables.

When possible, remove or simplify getNonIndexable() logic in fragments,
and use searchable="false" in xml to suppress index.

Change-Id: I5bdf5bc7d5494a64cdd9e230a51321a4b210af69
Fixes: 112608186
Test: robotest and manual search

src/com/android/settings/notification/ZenModeRestrictNotificationsSettings.java

@@ -90,12 +90,6 @@ public class ZenModeRestrictNotificationsSettings extends ZenModeSettingsBase im
                     return result;
                 }
 
-                @Override
-                public List<String> getNonIndexableKeys(Context context) {
-                    final List<String> keys = super.getNonIndexableKeys(context);
-                    return keys;
-                }
-
             @Override
             public List<AbstractPreferenceController> createPreferenceControllers(Context context) {
                 return buildPreferenceControllers(context, null);