remove unusing directive

Author: smdn

src/Smdn.Fundamental.Uuid/Smdn/Uuid.cs

@@ -2,7 +2,6 @@
 // SPDX-License-Identifier: MIT
 using System;
 using System.Buffers.Binary;
-using System.Globalization;
 #if SYSTEM_NET_NETWORKINFORMATION_PHYSICALADDRESS
 using System.Net.NetworkInformation;
 #endif