Remove unneeded using.

Author: claudiamurialdo

dotnet/src/dotnetcore/GxNetCoreStartup/Startup.cs

@@ -30,7 +30,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.Logging;
-using Microsoft.Extensions.Options;
 using StackExchange.Redis;