fix(cert_manager): stop deleting the namespace on every upgrade run (#13493)

The "Remove legacy namespace" task unconditionally ran
kubectl delete namespace on every playbook run carrying the upgrade
tag, wiping user-managed resources in the cert-manager namespace (for
example custom Issuer secrets) as well as cert-manager's own state,
before the namespace was recreated and the manifests re-applied.

The legacy addon migration this cleanup was written for dates back to
2018 and no longer applies; the apply path (kube module, state latest)
upgrades cert-manager in place without a namespace reset.

Signed-off-by: longyuxiang <longyuxiang@kylinos.cn>

roles/kubernetes-apps/ingress_controller/cert_manager/tasks/main.yml

@@ -9,15 +9,6 @@
   tags:
     - upgrade
 
-- name: Cert Manager | Remove legacy namespace
-  command: >
-    {{ kubectl }} delete namespace {{ cert_manager_namespace }}
-  ignore_errors: true  # noqa ignore-errors
-  when:
-    - inventory_hostname == groups['kube_control_plane'][0]
-  tags:
-    - upgrade
-
 - name: Cert Manager | Create addon dir
   file:
     path: "{{ kube_config_dir }}/addons/cert_manager"