Remove unused usings

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RenameDocumentUndoUnit.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;
-using System.Collections.Generic;
 using System.Linq;
-using Microsoft.CodeAnalysis;
 using Microsoft.VisualStudio.OLE.Interop;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem