Delete spec.disableServerTags of OpenStackCluster

Spec.disableServerTags of OpenStackCluster is deleted in
e58572d. But
cluster-template-external-cloud-provider.yaml was missed.
This commit deletes it.

Author: hidekazuna

templates/cluster-template-external-cloud-provider.yaml

@@ -32,7 +32,6 @@ spec:
   dnsNameservers:
   - ${OPENSTACK_DNS_NAMESERVERS}
   disablePortSecurity: false
-  disableServerTags: true
   useOctavia: true
 ---
 kind: KubeadmControlPlane