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/system/ResetPreferenceController.java

@@ -29,7 +29,7 @@ public class ResetPreferenceController extends BasePreferenceController {
     @Override
     public int getAvailabilityStatus() {
         return mContext.getResources().getBoolean(R.bool.config_show_reset_dashboard)
-                ? AVAILABLE
+                ? AVAILABLE_UNSEARCHABLE
                 : UNSUPPORTED_ON_DEVICE;
     }
 }