Micro cleanup and refactoring

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

Test: robotest
Change-Id: I1a5a49bee1c4edb34f1c59f3dbe37cb22f01b0d4

src/com/android/settings/DateTimeSettings.java

@@ -20,7 +20,6 @@ import android.app.Activity;
 import android.app.Dialog;
 import android.content.Context;
 import android.content.Intent;
-import android.os.UserManager;
 import android.provider.SearchIndexableResource;
 
 import com.android.internal.logging.nano.MetricsProto.MetricsEvent;