vagrant: Don't modify /etc/security/access.conf

https://salsa.debian.org/freedombox-team/freedom-maker/-/blob/master/bin/vagrant-package#L142

This file will no longer exist due to freedombox!2309 (closed).

We also need to ensure that the vagrant user can login through SSH. We can add it to one of the allowed groups: https://salsa.debian.org/freedombox-team/freedombox/-/blob/master/plinth/modules/ssh/privileged.py#L65