Don't set the item variable as eager template replacement will over-replace the variable as an empty string.
Playbook + with_items was an undocumented feature that was causing problems because it would
evaluate and replace '$item' with ''.  Really it doesn't make sense to include multiple playbooks
via a loop variable, as you can do this with task + with_items already (and it's a simpler code
path).  Given this is undocumented, this removes that feature, and we'll consider next how to
also add 'with_items' support directly to roles.