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/connecteddevice/usb/UsbDetailsFragment.java

@@ -113,11 +113,6 @@ public class UsbDetailsFragment extends DashboardFragment {
                     return Lists.newArrayList(res);
                 }
 
-                @Override
-                public List<String> getNonIndexableKeys(Context context) {
-                    return super.getNonIndexableKeys(context);
-                }
-
                 @Override
                 public List<AbstractPreferenceController> createPreferenceControllers(
                         Context context) {