Remove dupe using

Author: dougbu

src/Components/test/E2ETest/ServerExecutionTests/CircuitGracefulTerminationTests.cs

@@ -5,7 +5,6 @@
 using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
 using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
 using Microsoft.AspNetCore.E2ETesting;
-using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging.Testing;
 using Microsoft.AspNetCore.Testing;