Remove unused System.Diagnostics import

Author: SimaTian

src/Shared/LogMessagePacketBase.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
@@ -18,8 +18,6 @@
 using Microsoft.Build.Framework.Profiler;
 using System.Collections;
 using System.Linq;
-using System.Diagnostics;
-
 #endif
 
 #if FEATURE_APPDOMAIN