Remove veth cleanup code

This is panicking because the veth name doesn't match the name in the
container. It also leaks the network namespace, and isn't necessary once
firecracker-microvm/firecracker-go-sdk#428 is
in.

driver/handle.go

@@ -27,7 +27,6 @@ import (
 	"github.com/hashicorp/nomad/client/stats"
 	"github.com/hashicorp/nomad/plugins/drivers"
 	"github.com/shirou/gopsutil/process"
-	"github.com/vishvananda/netlink"
 )
 
 var (
@@ -220,11 +219,6 @@ func (h *taskHandle) Signal(sig string) error {
 // shutdown shuts down the container, with `timeout` grace period
 // before shutdown vm
 func (h *taskHandle) shutdown(timeout time.Duration) error {
-	vnic, _ := netlink.LinkByName(h.Info.Vnic)
-	err := netlink.LinkDel(vnic)
-	if err != nil {
-			h.logger.Error("unable to remove veth ", h.Info.Vnic, " from ", h.taskConfig.ID)
-	}
 	time.Sleep(timeout)
 	h.MachineInstance.StopVMM()
 	return nil