I’ve found it!
For the future seraches. Change line 563 on links.php from this:
// Display the category name echo ' <li id="'.sanitize_title($cat['cat_name']).'">' . stripslashes($cat['cat_name']) . "\n\t
To this:
// Display the category name echo ' <!--<li id="'.sanitize_title($cat['cat_name']).'">-->' . stripslashes($cat['cat_name']) . "\n\t