drop dependency on xcp

It's actually not faster in combination with xargs...

disko-install

@@ -235,12 +235,8 @@ main() {
   if [[ ! -d "${mountPoint}/nix/store" ]]; then
     export NIX_STATE_DIR=${mountPoint}/nix/var/nix
     echo "Copying store paths" >&2
-
-    if [ -t 1 ]; then
-      xargs -I% xcp --recursive % "${mountPoint}/nix/store" < "${closure_info}/store-paths"
-    else
-      xargs -I% xcp --recursive --no-progress % "${mountPoint}/nix/store" < "${closure_info}/store-paths"
-    fi
+    mkdir -p "${mountPoint}/nix/store"
+    xargs cp --recursive --target "${mountPoint}/nix/store"  < "${closure_info}/store-paths"
     echo "Loading nix database" >&2
     nix-store --load-db < "${closure_info}/registration"
     unset NIX_STATE_DIR

lib/make-disk-image.nix

@@ -28,7 +28,6 @@ let
     systemdMinimal
     nix
     util-linux
-    xcp
   ] ++ nixosConfig.config.disko.extraDependencies;
   preVM = ''
     ${lib.concatMapStringsSep "\n" (disk: "truncate -s ${disk.imageSize} ${disk.name}.raw") (lib.attrValues nixosConfig.config.disko.devices.disk)}
@@ -68,7 +67,7 @@ let
 
     # We copy files with cp because `nix copy` seems to have a large memory leak
     mkdir -p ${systemToInstall.config.disko.rootMountPoint}/nix/store
-    xargs -I % xcp --recursive % ${systemToInstall.config.disko.rootMountPoint}/nix/store < ${closureInfo}/store-paths
+    xargs cp --recursive --target ${systemToInstall.config.disko.rootMountPoint}/nix/store < ${closureInfo}/store-paths
 
     ${systemToInstall.config.system.build.nixos-install}/bin/nixos-install --root ${systemToInstall.config.disko.rootMountPoint} --system ${systemToInstall.config.system.build.toplevel} --keep-going --no-channel-copy -v --no-root-password --option binary-caches ""
     umount -Rv ${systemToInstall.config.disko.rootMountPoint}