Removed the unnecessary comment.

Author: mkArtakMSFT

src/Mvc/Mvc.Testing.Tasks/src/GenerateMvcTestManifestTask.cs

@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-//using System;
 using System;
 using System.Collections.Generic;
 using System.IO;