nixos/make-ext4-fs: Use closureInfo

exportReferencesGraph is deprecated and doesn't have the generated
initial Nix database contain the SHA256 of the contents of the store
paths, which breaks various things under Nix 2.0.

nixos/lib/make-ext4-fs.nix

@@ -7,23 +7,22 @@
 , volumeLabel
 }:
 
+let
+  sdClosureInfo = pkgs.closureInfo { rootPaths = storePaths; };
+in
+
 pkgs.stdenv.mkDerivation {
   name = "ext4-fs.img";
 
   nativeBuildInputs = with pkgs; [e2fsprogs libfaketime perl];
 
-  # For obtaining the closure of `storePaths'.
-  exportReferencesGraph =
-    map (x: [("closure-" + baseNameOf x) x]) storePaths;
-
   buildCommand =
     ''
       # Add the closures of the top-level store objects.
-      storePaths=$(perl ${pkgs.pathsFromGraph} closure-*)
+      storePaths=$(cat ${sdClosureInfo}/store-paths)
 
-      # Also include a manifest of the closures in a format suitable
-      # for nix-store --load-db.
-      printRegistration=1 perl ${pkgs.pathsFromGraph} closure-* > nix-path-registration
+      # Also include a manifest of the closures in a format suitable for nix-store --load-db.
+      cp ${sdClosureInfo}/registration nix-path-registration
 
       # Make a crude approximation of the size of the target image.
       # If the script starts failing, increase the fudge factors here.