refactor(aspen/orgExportHTML): use default emacs

In r/4000, I switched orgExportHTML to Emacs 28 (which bundles org by
default) when nixpkgs defaulted to Emacs 27. Since nixpkgs now uses
Emacs 29 by default, this is no longer necessary.

Change-Id: I6d700e8508be77a1b9866557403a5a4ecaa005f7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12569
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: aspen <root@gws.fyi>

users/aspen/web/orgExportHTML.nix

@@ -3,12 +3,6 @@
 with pkgs;
 with lib;
 
-let
-
-  emacs = pkgs.emacs28;
-
-in
-
 opts:
 
 let
@@ -42,7 +36,7 @@ in
 runCommand outName { inherit src; } ''
   buildFile() {
     cp "$1" file.org
-    ${emacs}/bin/emacs --batch \
+    ${pkgs.emacs}/bin/emacs --batch \
       --load ${./config.el} \
       --visit file.org \
       --eval "(progn