Improve Search results highlighting

- remove unnecessary code
- use keyed Tag with a well known App key for preventing collisions
- fix missing Brightness Level preference key (used for highlight)

Change-Id: Ib856cc33f9058c10303d239e60a0ee4c322385a1

res/xml/display_settings.xml

@@ -19,6 +19,7 @@
         xmlns:settings="http://schemas.android.com/apk/res/com.android.settings">
 
         <com.android.settings.BrightnessPreference
+                android:key="brightness"
                 android:title="@string/brightness"
                 android:persistent="false"/>