removing deprecated beta prefix

Author: Gordon Byers

articles/aks/virtual-nodes-cli.md

@@ -162,7 +162,7 @@ spec:
         - containerPort: 80
       nodeSelector:
         kubernetes.io/role: agent
-        beta.kubernetes.io/os: linux
+        kubernetes.io/os: linux
         type: virtual-kubelet
       tolerations:
       - key: virtual-kubelet.io/provider