haskellPackages.cabal2nix-unstable: don't wrap with runtime deps

cabal2nix-unstable is mostly used for regenerating the Haskell package
set. Thus we should aim to make it quick to rebuild in case its hash
changes because of Haskell related changes.

- cabal2nix is not fussy about the Nix version it uses for nix-env(1)
  and we can just assume it is already in PATH like we do for
  maintainers/scripts/haskell/*.

- nix-prefetch-scripts causes the most trouble since its python
  dependencies depend on pandoc, so many Haskell changes require
  an additional Python rebuild when building cabal2nix-unstable.

  nix-prefetch-scripts is most likely installed and not necessary in
  many cases, e.g. hackage2nix doesn't need them which is the main use
  we have for cabal2nix-unstable. For the update scripts that do need
  them, we add them to the used nix-shell explicitly.

maintainers/scripts/haskell/update-cabal2nix-unstable.sh

@@ -1,5 +1,5 @@
 #! /usr/bin/env nix-shell
-#! nix-shell -i bash -p coreutils curl jq gnused haskellPackages.cabal2nix-unstable.bin -I nixpkgs=.
+#! nix-shell -i bash -p coreutils curl jq gnused haskellPackages.cabal2nix-unstable.bin nix-prefetch-scripts -I nixpkgs=.
 
 # Updates cabal2nix-unstable to the latest master of the nixos/cabal2nix repository.
 # See regenerate-hackage-packages.sh for details on the purpose of this script.

pkgs/development/haskell-modules/configuration-nix.nix

@@ -1260,21 +1260,6 @@ builtins.intersectAttrs super {
   # not used to link against by anyone, we can make it’s closure smaller and
   # add its runtime dependencies in `haskellPackages` (as opposed to cabal2nix).
   cabal2nix-unstable = overrideCabal (drv: {
-    buildTools = (drv.buildTools or [ ]) ++ [
-      pkgs.buildPackages.makeWrapper
-    ];
-    postInstall = ''
-      ${drv.postInstall or ""}
-
-      wrapProgram $out/bin/cabal2nix \
-        --prefix PATH ":" "${
-          pkgs.lib.makeBinPath [
-            pkgs.nix
-            pkgs.nix-prefetch-scripts
-          ]
-        }"
-    '';
-
     passthru = drv.passthru or { } // {
       updateScript = ../../../maintainers/scripts/haskell/update-cabal2nix-unstable.sh;
 

pkgs/development/tools/purescript/spago/update.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p cabal2nix curl jq haskellPackages.cabal2nix-unstable.bin -I nixpkgs=.
+#!nix-shell -i bash -p cabal2nix curl jq haskellPackages.cabal2nix-unstable.bin nix-prefetch-scripts -I nixpkgs=.
 #
 # This script will update the spago derivation to the latest version using
 # cabal2nix.