nh-unwrapped: fix postInstall cleanup (#500839)

  nativeInstallCheckInputs = [ versionCheckHook ];

  postInstall = lib.optionalString (stdenv.hostPlatform.emulatorAvailable buildPackages) ''

  postInstall =

    lib.optionalString (stdenv.hostPlatform.emulatorAvailable buildPackages) (

      let

        emulator = stdenv.hostPlatform.emulator buildPackages;

      in

      ''

        # Run both shell completion and manpage generation tasks. Unlike the

        # fine-grained variants, the 'dist' command doesn't allow specifying the

        # path but that's fine, because we can simply install them from the implicit

        # output directories.

    $out/bin/xtask dist

        ${emulator} $out/bin/xtask dist

        # The dist task above should've created

        #  1. Shell completions in comp/

        # about what we're installing, or this will fail.

        installShellCompletion --cmd ${finalAttrs.meta.mainProgram} ./comp/*.{bash,fish,zsh,nu}

        installManPage ./man/nh.1

      ''

    )

    + ''

      # Avoid populating PATH with an 'xtask' cmd

      rm $out/bin/xtask

    '';