Remove unused using

Author: alanwest

src/OpenTelemetry.Instrumentation.Http/Implementation/HttpHandlerDiagnosticListener.cs

@@ -17,7 +17,6 @@
 using System;
 using System.Diagnostics;
 using System.Net.Http;
-using System.Net.Sockets;
 using System.Reflection;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;