remove nix support (#47)

Nix is not supposed to be used on NixOS the way that cpm implements it,
and it's (to the best of my knowledge) not the best way on other
platforms as well. We also do not support non-platform-specific package
managers, so the precedent says we should remove this one.

README.md

@@ -29,7 +29,6 @@ $ cpm [i|r|l|u|U|s|S|I|F|f|c|h] [pkg]...
 - dnf (Fedora)
 - lunar (Lunar Linux)
 - MacPorts (MacOS)
-- nix (Global/NixOS)
 - guix (non-system-wide Guix)
 - pacman (Arch)
 - slackpkg (Slackware)
@@ -43,6 +42,7 @@ $ cpm [i|r|l|u|U|s|S|I|F|f|c|h] [pkg]...
 - Cargo
 - Flatpak
 - Homebrew
+- Nix
 - NPM
 - Pip
 - Snap

cpm

@@ -400,21 +400,6 @@ _guix() {
   esac
 }
 
-_nix() {
-  case "$OP" in
-    install) nix-env -iA "$@";;
-    remove)  niv-env -e "$@";;
-    list)    nix-env -q "$@";;
-    count)   nix-env -q | tot;;
-    update)  nix-channel --update;;
-    upgrade) nix-env -u;;
-    search)  nix-env -qa "$@";;
-    show)    nix-env -qa --description "$@";;
-    f*)      pem "unsupported: this feature is functionally useless in this PM";;
-    clean)   nix-collect-garbage -d;;
-  esac
-}
-
 # Use pm=PKG_MANAGER cpm COMMAND to force a specific cpm function
 # ie.: pm=portage cpm list
 if [ "$pm" ] && has "_$pm"; then
@@ -455,9 +440,6 @@ elif has sorcery; then
 elif has lunar; then
   # lunar linux
   _lunar "$@"
-elif has nix; then
-  # global/nixos
-  _nix "$@"
 elif has guix; then
   # local (non-system-wide) guix
   _guix "$@"