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

src/com/android/settings/HighlightingFragment.java

@@ -116,7 +116,7 @@ public class HighlightingFragment extends Fragment {
     }
 
     private boolean checkTag(View view, String key) {
-        final Object tag = view.getTag();
+        final Object tag = view.getTag(R.id.preference_highlight_key);
         if (tag == null || !(tag instanceof String)) {
             return false;
         }