docker-machine-hyperkit: disable on aarch64-darwin

It's not supported in upstream, see
https://github.com/kubernetes/minikube/blob/master/pkg/minikube/driver/driver_darwin.go#L27-L35

pkgs/applications/networking/cluster/docker-machine/hyperkit.nix

···
     description = "HyperKit driver for docker-machine";
     license = licenses.asl20;
     maintainers = with maintainers; [ atkinschang ];
-    platforms = platforms.darwin;
+    platforms = [ "x86_64-darwin" ];
   };
 }