Remove using statement

Author: ladeak

src/Servers/Kestrel/Core/src/Internal/Http/PathNormalizer.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
 using Microsoft.AspNetCore.Internal;