Remove Kubelet --network-plugin=cni flag

* Now that `docker-shim` is no longer used, the Kubelet flag
is no longer needed and will be removed in v1.24

google-cloud/flatcar-linux/kubernetes/workers/cl/worker.yaml

@@ -67,7 +67,6 @@ systemd:
           --cluster_domain=${cluster_domain_suffix} \
           --healthz-port=0 \
           --kubeconfig=/var/lib/kubelet/kubeconfig \
-          --network-plugin=cni \
           --node-labels=node.kubernetes.io/node \
           %{~ for label in split(",", node_labels) ~}
           --node-labels=${label} \