xdg-desktop-portal-phosh: drop incorrect updateScript

The update script fails to eval:

    $ nix-shell maintainers/scripts/update.nix --argstr package xdg-desktop-portal-phosh
    error:
       … while calling the 'derivationStrict' builtin
         at «nix-internal»/derivation-internal.nix:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'nixpkgs-update-script'
         whose name attribute is located at pkgs/stdenv/generic/make-derivation.nix:544:13

       … while evaluating attribute 'shellHook' of derivation 'nixpkgs-update-script'
         at maintainers/scripts/update.nix:275:3:
          274|   '';
          275|   shellHook = ''
             |   ^
          276|     unset shellHook # do not contaminate nested shells

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'updateScript' missing
       at pkgs/by-name/xd/xdg-desktop-portal-phosh/package.nix:76:20:
           75|   passthru = {
           76|     updateScript = lib.updateScript { };
             |                    ^
           77|   };

pkgs/by-name/xd/xdg-desktop-portal-phosh/package.nix

@@ -72,10 +72,6 @@ stdenv.mkDerivation (finalAttrs: {
     ./cargo_lock_deps_version.patch
   ];
 
-  passthru = {
-    updateScript = lib.updateScript { };
-  };
-
   meta = with lib; {
     description = "A backend implementation for xdg-desktop-portal that is using GTK/GNOME/Phosh to provide interfaces that aren't provided by the GTK portal";
     homepage = "https://gitlab.gnome.org/guidog/xdg-desktop-portal-phosh";