Remove website URL field from WordPress comment form. Source: https://wordpress.org/support/topic/remove-url-and-email-fields-from-comments-form#post-3956088

custom-comment-fields.php

<?php

//* Remove both website and email fields from WordPress comment form
function prefix_custom_comment_fields($fields) {
    unset($fields['url']);
    unset($fields['email']);
    return $fields;
}
add_filter('comment_form_default_fields', 'prefix_custom_comment_fields');

remove-website-url-field-from-comment-form.php

<?php

//* Remove website URL field from WordPress comment form
function prefix_remove_website_field($fields) {
    unset($fields['url']);
    return $fields;
}
add_filter('comment_form_default_fields', 'prefix_remove_website_field');