Replacing default user is not idempotent

[colin-nolan]

Creating a new user to replace the default one should be idempotent (i.e. should not use changed_when: True): https://github.com/mikolak-net/ansible-raspi-config/blob/85cae51462822d9a5fe083f9effc6d4cfe433e5b/tasks/setup_replace_user.yml#L3-L8.

I think the step to remove the default user can just be a normal task, not a handler.