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/display/AutoBrightnessPreferenceController.java

@@ -52,7 +52,7 @@ public class AutoBrightnessPreferenceController extends TogglePreferenceControll
     public int getAvailabilityStatus() {
         return mContext.getResources().getBoolean(
                 com.android.internal.R.bool.config_automatic_brightness_available)
-                ? AVAILABLE
+                ? AVAILABLE_UNSEARCHABLE
                 : UNSUPPORTED_ON_DEVICE;
     }