nixos: use Dhall VFS library in store-wrapper

nixos-modules/store-wrapper.dhall

@@ -48,16 +48,13 @@ in  λ(subinit : Init.Type) →
                         , binary = "vfs"
                         , config = Init.Config::{
                           , content =
-                            [ XML.element
+                              let VFS = Genode.VFS
-                                { name = "vfs"
+
-                                , attributes = XML.emptyAttributes
+                              in  [ VFS.vfs
-                                , content =
+                                      [ VFS.leafAttrs
-                                  [ XML.leaf
+                                          "tar"
-                                      { name = "tar"
+                                          (toMap { name = storeName })
-                                      , attributes = toMap { name = storeName }
-                                      }
                                       ]
-                                }
                                   ]
                           , policies =
                             [ Init.Config.Policy::{