Remove unnecessary usings

src/Compilers/CSharp/Test/Emit/Emit/EditAndContinue/EditAndContinueClosureTests.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System.Collections.Immutable;
-using System.IO;
 using System.Linq;
 using System.Reflection.Metadata.Ecma335;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
@@ -10,7 +9,6 @@
 using Microsoft.CodeAnalysis.Emit;
 using Microsoft.CodeAnalysis.Test.Utilities;
 using Roslyn.Test.Utilities;
-using Roslyn.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.CSharp.EditAndContinue.UnitTests