Remove OSNotificationOpenedHandler from NotificationServiceExtension

* Add setNotificationOpenedHandler on Example App
* Remove OSNotificationOpenedHandler from NotificationServiceExtension to avoid user confusion

Author: Jeasmine

Examples/OneSignalDemo/app/src/main/java/com/onesignal/sdktest/application/MainApplication.java

@@ -4,6 +4,7 @@
 import android.util.Log;
 
 import com.onesignal.OSNotification;
+import com.onesignal.OSNotificationOpenedResult;
 import com.onesignal.OneSignal;
 import com.onesignal.sdktest.R;
 import com.onesignal.sdktest.constant.Tag;
@@ -31,6 +32,9 @@ public void onCreate() {
         OneSignal.setAppId(appId);
         OneSignal.initWithContext(this);
 
+        OneSignal.setNotificationOpenedHandler(result ->
+                OneSignal.onesignalLog(OneSignal.LOG_LEVEL.VERBOSE, "OSNotificationOpenedResult result: " + result.toString()));
+
         OneSignal.setNotificationWillShowInForegroundHandler(notificationReceivedEvent -> {
             OneSignal.onesignalLog(OneSignal.LOG_LEVEL.VERBOSE, "NotificationWillShowInForegroundHandler fired!" +
                     " with notification event: " + notificationReceivedEvent.toString());

Examples/OneSignalDemo/app/src/main/java/com/onesignal/sdktest/notification/NotificationServiceExtension.java

@@ -10,8 +10,7 @@
 import com.onesignal.sdktest.R;
 
 public class NotificationServiceExtension implements
-        OneSignal.OSRemoteNotificationReceivedHandler,
-        OneSignal.OSNotificationOpenedHandler {
+        OneSignal.OSRemoteNotificationReceivedHandler {
 
    @Override
    public void remoteNotificationReceived(Context context, OSNotificationReceivedEvent notificationReceivedEvent) {
@@ -33,8 +32,4 @@ public void remoteNotificationReceived(Context context, OSNotificationReceivedEv
       notificationReceivedEvent.complete(mutableNotification);
    }
 
-   @Override
-   public void notificationOpened(OSNotificationOpenedResult result) {
-      OneSignal.onesignalLog(OneSignal.LOG_LEVEL.VERBOSE, "OSNotificationOpenedResult result: " + result.toString());
-   }
 }