Remove unnecessary usings

Author: kzu

src/GrokClient/Extensions.cs

@@ -1,7 +1,4 @@
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Threading;
-using System.Threading.Tasks;
+using System.ComponentModel;
 using Google.Protobuf.WellKnownTypes;
 
 namespace Devlooped.Grok;