How to remove website url field from comment form completely?

The code you’ve provided does remove the website URL field from the comment form. However, bots can still directly POST to the wp-comments-post.php file with a URL included. To prevent this, you can remove the URL from the submitted data before it’s saved to the database. You can achieve this using the preprocess_comment filter.

Add the following code to your theme’s functions.php file:

function xyzmark_remove_comment_author_url( $commentdata ) {
    $commentdata['comment_author_url'] = ''; // remove the URL from the submitted data
    return $commentdata;
add_filter('preprocess_comment', 'xyzmark_remove_comment_author_url');

This code will ensure that even if someone (or a bot) directly submits a comment with a URL, it will be removed before the comment data is saved. Note that this won’t affect the ability of admins to manually add URLs to comments from within the WordPress admin interface.