Plugin shows authors not added to post

The Coauthors plus plugin is showing authors who haven’t been added to a post. Ideally, I’d like to remove the plugin, but the developer who is no longer attached the the project has integrated it across several files and disabling the plugin causes the entire post content to vanish.

But how can I get it to simply show only the authors who should be visible and not the others.

?php if (have_posts()) : while (have_posts()) : the_post(); ?>
                        <?php
                        global $coauthors_plus;
                        $local_post = get_post();
                        $coauthor_terms = wp_get_post_terms($local_post->ID, $coauthors_plus->coauthor_taxonomy, array(
                            'orderby' => 'name',
                            'hide_empty' => true,
                            'number' => 5,
                        ));
                        ?>

I’d seen elsewhere that if you add register_taxonomy( 'author', array( 'post' ) ); to your functions.php file while the plugin is disabled then you should get an admin interface where you can delete existing Co-Authors Plus terms, but I have added this to the functions.php file and have not seen any such interface within WordPress.

Any assist greatly appreciated.