Remove deprecated key from kubeadmconfig/v1beta4 (#11709)

timeoutForControlPlane has been removed from v1beta4, instead remplaced
by https://kubernetes.io/docs/reference/config-api/kubeadm-config.v1beta4/#kubeadm-k8s-io-v1beta4-Timeouts

The default for the new value are close enough that there is no need to
override them.