Remove unused usings (#2217)

Source/MQTTnet.Tests/Formatter/MqttBufferReader_Tests.cs

@@ -2,10 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
-using System.Collections.Generic;
-using System.IO;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Binary_Tests.cs

@@ -2,11 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
 using System.Buffers;
-using System.IO;
-using System.Threading;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics.Logger;
 using MQTTnet.Exceptions;

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -2,9 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
 using System.Buffers;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

@@ -2,9 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
 using System.Buffers;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Formatter;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;

Source/MQTTnet.Tests/Formatter/MqttPacketWriter_Tests.cs

@@ -1,5 +1,3 @@
-using System;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;