s/apiservers/api_servers/ in Salt

It looks like api_servers finally won this battle. Kill off the
last remaining places passing it, but allow the kubelet Salt to
accept apiservers for a period of time.

(This was bothering my OCD.)

cluster/gce/configure-vm.sh

@@ -343,7 +343,6 @@ function salt-set-apiserver() {
 
   cat <<EOF >>/etc/salt/minion.d/grains.conf
   api_servers: '${kube_master_fqdn}'
-  apiservers: '${kube_master_fqdn}'
 EOF
 }