Remove parallel join note

Co-authored-by: Lubomir I. Ivanov <[email protected]>

Author: ramalabeysekera

content/en/docs/setup/production-environment/tools/kubeadm/high-availability.md

@@ -263,7 +263,6 @@ For each additional control plane node you should:
    - The `--certificate-key ...` will cause the control plane certificates to be downloaded
      from the `kubeadm-certs` Secret in the cluster and be decrypted using the given key.
 
-You can join multiple control-plane nodes in parallel.
 
 {{< note >}}
 As the cluster nodes are usually initialized sequentially, the CoreDNS Pods are likely to all run