remove usage of the "certificates" API for cert renewal (#26841)

* remove usage of the "certificates" API for cert renewal

"--use-api" option is removed from kubeadm alpha certs renew command since k8s 1.19

* Update kubeadm-certs.md

* Update content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md

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

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

Author: tibetsam

content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md

@@ -170,36 +170,7 @@ controllerManager:
 
 ### Create certificate signing requests (CSR)
 
-You can create the certificate signing requests for the Kubernetes certificates API with `kubeadm certs renew --use-api`.
-
-If you set up an external signer such as [cert-manager](https://github.com/jetstack/cert-manager), certificate signing requests (CSRs) are automatically approved.
-Otherwise, you must manually approve certificates with the [`kubectl certificate`](/docs/setup/best-practices/certificates/) command.
-The following kubeadm command outputs the name of the certificate to approve, then blocks and waits for approval to occur:
-
-```shell
-sudo kubeadm certs renew apiserver --use-api &
-```
-The output is similar to this:
-```
-[1] 2890
-[certs] certificate request "kubeadm-cert-kube-apiserver-ld526" created
-```
-
-### Approve certificate signing requests (CSR)
-
-If you set up an external signer, certificate signing requests (CSRs) are automatically approved.
-
-Otherwise, you must manually approve certificates with the [`kubectl certificate`](/docs/setup/best-practices/certificates/) command. e.g.
-
-```shell
-kubectl certificate approve kubeadm-cert-kube-apiserver-ld526
-```
-The output is similar to this:
-```shell
-certificatesigningrequest.certificates.k8s.io/kubeadm-cert-kube-apiserver-ld526 approved
-```
-
-You can view a list of pending certificates with `kubectl get csr`.
+See [Create CertificateSigningRequest](https://kubernetes.io/docs/reference/access-authn-authz/certificate-signing-requests/#create-certificatesigningrequest) for creating CSRs with the Kubernetes API.
 
 ## Renew certificates with external CA