Revert "nixos: set nixos in nixPath"
Revert "nixos: set nixos in nixPath"

This reverts commit 67c8c4917799496dcf2ad6a500441fbbaeb918c9.

'nix run nixos.firefox' is *not* supposed to work - the Nix 2.x
interface attempts to standardize on nixpkgs.*, to get rid of the
nixos/nixpkgs confusion that existed with the channels interface. So
let's not bring that confusion back.

SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs