Remove unnecessary usings

src/EditorFeatures/Core/Implementation/CodeFixes/CodeFixService.cs

@@ -5,7 +5,6 @@
 using System.Collections.Immutable;
 using System.Composition;
 using System.Diagnostics;
-using System.Diagnostics.Tracing;
 using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Threading;

src/Features/Core/Portable/CodeRefactorings/CodeRefactoringService.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Composition;
-using System.Diagnostics.Tracing;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;

src/Workspaces/Core/Portable/Workspace/Host/SyntaxTreeFactory/AbstractSyntaxTreeFactoryService.AbstractRecoverableSyntaxRoot.cs

@@ -3,7 +3,6 @@
 using System;
 using System.Collections.Immutable;
 using System.Diagnostics;
-using System.Diagnostics.Tracing;
 using System.IO;
 using System.Text;
 using System.Threading;