[occm] docs: remove deprecated apiserver flag from kubeadm.conf (#2899)

Author: jxadl

manifests/controller-manager/kubeadm.conf

@@ -11,9 +11,6 @@ kind: ClusterConfiguration
 kubernetesVersion: v1.17.0
 networking:
   podSubnet: 192.168.0.0/16
-apiServer:
-  extraArgs:
-    cloud-provider: "external"
 controllerManager:
   extraArgs:
     cloud-provider: "external"