Remove outdated Vagrantfile

[dbaty]

Description

It mentions Debian 10 (released in 2019) and Centos 7.9 (released in 2020). To put it mildly: it is unlikely to have been used recently.

I also removed mention of this file in the contribution documentation: Debian, Fedora and other package maintainers most probably use something else.

Checklist

• [] I've added this contribution to the changelog.rst. Not added to the changelog, because this file is not shipped, it's merely provided wit the sources.
• I've added my name to the AUTHORS file (or it's already there).
• I installed pre-commit hooks (pip install pre-commit && pre-commit install).
• I verified that my changes work as expected (this may include manually testing them in your local environment, or in other available environments). Cross this out if not relevant (for example, if you're making a documentation change).
• [] Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)