feat: comment out nixpkgs-unstable, we use unstable by default

Signed-off-by: Ryan Yin <xiaoyin_c@qq.com>

modules/darwin/apps.nix

@@ -2,7 +2,6 @@
   config,
   lib,
   pkgs,
-  pkgs-unstable,
   ...
 }:
 ##########################################################################
@@ -95,7 +94,7 @@ in
   programs.zsh.enable = true;
   environment.shells = [
     pkgs.zsh
-    pkgs-unstable.nushell # my custom shell
+    pkgs.nushell # my custom shell
   ];
 
   # homebrew need to be installed manually, see https://brew.sh

modules/nixos/desktop/misc.nix

@@ -1,8 +1,6 @@
 {
-  config,
   lib,
   pkgs,
-  pkgs-unstable,
   ...
 }:
 {

modules/nixos/desktop/peripherals.nix

@@ -15,7 +15,6 @@
   #     https://nixos.wiki/wiki/PipeWire
   services.pipewire = {
     enable = true;
-    # package = pkgs-unstable.pipewire;
     alsa.enable = true;
     alsa.support32Bit = true;
     pulse.enable = true;