This removes the dependency on the `nixpkgs` channel within the
modules for state version ≥ 20.09. The default Nixpkgs source starting
from this state version is the path of the `pkgs` argument used to
bootstrap the Home Manager modeuls.
This is a prerequisite for using Home Manager withing Nix flakes.
PR #1420
This allows pkgs to be overridden in such a way that `<nixpkgs>` is
never imported, allowing home-manager to be used in environments where
`NIX_PATH` is not set.
PR #993
On non-x86 architectures (for example, aarch64) the installation of
home-manager fails indicating that it is attempting to select i686
packages for Linux and those aren't available.
Solution: make the condition for choosing these packages stricter
