Micro cleanup and refactoring

- organize import
- remove unused code in ContextualCardLoaderTest
- refactor CardDatabaseHelper

Test: robotest
Change-Id: I1a5a49bee1c4edb34f1c59f3dbe37cb22f01b0d4

src/com/android/settings/homepage/contextualcards/CardDatabaseHelper.java

@@ -197,12 +197,11 @@ public class CardDatabaseHelper extends SQLiteOpenHelper {
     }
 
     Cursor getContextualCards() {
-        final SQLiteDatabase db = this.getReadableDatabase();
+        final SQLiteDatabase db = getReadableDatabase();
         final String selection = CardColumns.CARD_DISMISSED + "=0";
-        Cursor cursor = db.query(CARD_TABLE, null /* columns */, selection,
+        return db.query(CARD_TABLE, null /* columns */, selection,
                 null /* selectionArgs */, null /* groupBy */, null /* having */,
                 CardColumns.SCORE + " DESC" /* orderBy */);
-        return cursor;
     }
 
     /**