Remove identity: SystemAssigned from mps in upgrade templates

Author: willie-yao

test/e2e/data/infrastructure-azure/v1.16.3/cluster-template-prow-machine-and-machine-pool.yaml

@@ -29,7 +29,6 @@ metadata:
   name: ${CLUSTER_NAME}-mp-0
   namespace: default
 spec:
-  identity: SystemAssigned
   location: ${AZURE_LOCATION}
   template:
     osDisk: