For brand new installations, neither NIX_LINK_NEW (`$XDG_STATE_HOME/nix/profile` or `~/.local/state/nix/profile`), nor NIX_LINK (`~/.nix-profile`) will exist. This restores functionality to nix-env, which is relied upon by GitHub Actions such as https://github.com/cachix/cachix-action and the Nixpkgs EditorConfig (and other) CI.