Removed unused using

Author: noellie-velez

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -11,7 +11,6 @@
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using Unity.Jobs;
-using Unity.Mathematics;
 using Unity.Netcode.Runtime;
 using Unity.Networking.Transport;
 using Unity.Networking.Transport.Error;