Remove copy-com.nix from the module list

This is proprietary software, and NixOS is intended as a free software
distribution. We currently don't have a mechanism like allowUnfree for
NixOS modules, so it's better to leave out modules for such
packages. Of couse, they can still be activated by doing:

  imports = [ <nixpkgs/nixos/services/networking/copy-com.nix ];