lua wrapper: Fix bash error

Recently, we made it harder for external code to use some stdenv-only bash
variables by unsetting them in [1] But Lua's `withPackages` was sourcing some
setup hooks in [2], which required those bash variables.

I say great! We caught something bad: Lua should use normal dependencies, even
though that is harder with `buildEnv`. Now it works that way, and everything is
fine.

[1]: https://github.com/NixOS/nixpkgs/blob/9d3911f806034197bb7ace586cc3696ffce7f447/pkgs/stdenv/generic/setup.sh#L574-L578

[2]: https://github.com/NixOS/nixpkgs/blob/9d3911f806034197bb7ace586cc3696ffce7f447/pkgs/development/interpreters/lua-5/wrapper.nix#L23-L27

CC @matthewbauer