Remove the home-grown "solution" that I had stolen from school (and
never used...) for project-local configuration.
Since [1], it is okay to use the built-in vim option for this, since it
only asks for user-input before trusting a file.
Since [2] they even support lua files!
[1]: https://github.com/neovim/neovim/pull/20956
[2]: https://github.com/neovim/neovim/pull/21436