Update KestrelMetrics.cs

Author: BrennanConroy

src/Servers/Kestrel/Core/src/Internal/Infrastructure/KestrelMetrics.cs

@@ -4,7 +4,6 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Metrics;
-using System.Net.Sockets;
 using System.Runtime.CompilerServices;
 using System.Security.Authentication;
 using Microsoft.AspNetCore.Connections;