Fix duplicate storage-backend (#3906)

roles/kubernetes/master/templates/kubeadm-config.v1alpha1.yaml.j2

@@ -68,7 +68,6 @@ apiServerExtraArgs:
 {% if kube_version is version('v1.9', '>=') %}
   endpoint-reconciler-type: lease
 {% endif %}
-  storage-backend: etcd3
 {% if etcd_events_cluster_enabled %}
   etcd-servers-overrides: "/events#{{ etcd_events_access_addresses }}"
 {% endif %}

roles/kubernetes/master/templates/kubeadm-config.v1alpha2.yaml.j2

@@ -53,7 +53,6 @@ apiServerExtraArgs:
 {% if kube_version is version('v1.9', '>=') %}
   endpoint-reconciler-type: lease
 {% endif %}
-  storage-backend: etcd3
 {% if etcd_events_cluster_enabled %}
   etcd-servers-overrides: "/events#{{ etcd_events_access_addresses }}"
 {% endif %}

roles/kubernetes/master/templates/kubeadm-config.v1alpha3.yaml.j2

@@ -70,7 +70,6 @@ apiServerExtraArgs:
 {% if kube_version is version('v1.9', '>=') %}
   endpoint-reconciler-type: lease
 {% endif %}
-  storage-backend: etcd3
 {% if etcd_events_cluster_enabled %}
   etcd-servers-overrides: "/events#{{ etcd_events_access_addresses }}"
 {% endif %}

roles/kubernetes/master/templates/kubeadm-config.v1beta1.yaml.j2

@@ -68,7 +68,6 @@ apiServer:
 {% if kube_version is version('v1.9', '>=') %}
     endpoint-reconciler-type: lease
 {% endif %}
-    storage-backend: etcd3
 {% if etcd_events_cluster_enabled %}
     etcd-servers-overrides: "/events#{{ etcd_events_access_addresses }}"
 {% endif %}