chore(guix): remove the unused Guix integration

Guix was enabled on every desktop host, but shoukei had no /gnu mount (store and state lived on the tmpfs root) and it was not used. Drop the module, the modules.guix option, the @guix subvolume and the /var/guix preservation entry.

hosts/idols-ai/disko-fs.nix

@@ -87,13 +87,6 @@
                       "noatime"
                     ];
                   };
-                  "@guix" = {
-                    mountpoint = "/gnu";
-                    mountOptions = [
-                      "compress-force=zstd:1"
-                      "noatime"
-                    ];
-                  };
                   "@persistent" = {
                     mountpoint = "/persistent";
                     mountOptions = [

hosts/idols-ai/hardware-configuration.nix

@@ -74,7 +74,7 @@
     "exfat"
   ];
 
-  # LUKS initrd, all fileSystems (/, /boot, /btr_pool, /nix, /gnu, /persistent, /snapshots, /tmp, /swap)
+  # LUKS initrd, all fileSystems (/, /boot, /btr_pool, /nix, /persistent, /snapshots, /tmp, /swap)
   # and swap (including /swap/swapfile bind and swapDevices) are managed by disko (disko-fs.nix).
 
   # Enables DHCP on each ethernet and wireless interface. In case of scripted networking

modules/nixos/desktop/guix.nix

@@ -1,21 +0,0 @@
-{
-  # https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/guix/default.nix
-  services.guix = {
-    enable = true;
-    # The store directory where the Guix service will serve to/from.
-    # NOTE: most of the cached builds are assumed to be in `/gnu/store`.
-    storeDir = "/gnu/store";
-    # The state directory where Guix service will store its data such as its
-    # user-specific profiles, cache, and state files.
-    stateDir = "/var";
-    gc = {
-      enable = true;
-      # https://guix.gnu.org/en/manual/en/html_node/Invoking-guix-gc.html
-      extraArgs = [
-        "--delete-generations=1m"
-        "--free-space=10G"
-        "--optimize"
-      ];
-    };
-  };
-}