lisp/ox-html.el (org-html-scripts): Small refactoring

* lisp/ox-html.el (org-html-scripts): Small refactoring.

This replays the Javascript refactoring of commit 471054136.

Link: https://orgmode.org/list/498dbe2e-0cd2-c81e-7960-4a26c566a1f7@memebeam.org/

lisp/ox-html.el

@@ -240,19 +240,16 @@ property on the headline itself.")
      {
        var target = document.getElementById(id);
        if(null != target) {
-         elem.cacheClassElem = elem.className;
-         elem.cacheClassTarget = target.className;
-         target.className = \"code-highlighted\";
-         elem.className   = \"code-highlighted\";
+         elem.classList.add(\"code-highlighted\");
+         target.classList.add(\"code-highlighted\");
        }
      }
      function CodeHighlightOff(elem, id)
      {
        var target = document.getElementById(id);
-       if(elem.cacheClassElem)
-         elem.className = elem.cacheClassElem;
-       if(elem.cacheClassTarget)
-         target.className = elem.cacheClassTarget;
+       if(null != target) {
+         elem.classList.remove(\"code-highlighted\");
+         target.classList.remove(\"code-highlighted\");
      }
 // @license-end
 </script>"