We should not delete crd when uninstalling the Operator

https://docs.couchbase.com/operator/current/install-kubernetes.html#uninstalling-the-operator

Under the section of uninstalling the Operator, we gave this commend

$ kubectl delete -f crd.yaml

This is not needed and also dangerous to run since removing the crd would removing everything else on that cluster (cb server, PVs...). As we also mention that here

https://docs.couchbase.com/operator/current/howto-operator-upgrade.html#uninstall-operator

>Never delete existing CRDs. If an existing CRD is deleted, any CouchbaseCluster resources will also be deleted.

We should remove this command from the doc to avoid customer running it by mistake.