I’ve just checked your website; it appears you’re using a non-standard comment form; I note the class of your form element is “f1-comment-form” and not the standard “comment-form” class.
That could be because the theme you’re using is providing a non-standard comments form/system, or because you’re using a comments form plugin.
This plugin is only tested against the standard WordPress comments form.
If the plugin words for you in other respects, then you could remove the “website” field by modifying your comments form template – either in your plugin, or Theme.
Another option would be to simply hide the field using CSS, however this may not prohibit automated postings (bots), depending upon your overall security setup.
