Refactor code.

Source/MQTTnet/Client/MqttClient.cs

@@ -656,7 +656,7 @@ namespace MQTTnet.Client
             }
         }
 
-        internal Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs, CancellationToken cancellationToken)
+        Task AcknowledgeReceivedPublishPacket(MqttApplicationMessageReceivedEventArgs eventArgs, CancellationToken cancellationToken)
         {
             if (eventArgs.PublishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
             {