add_action( 'do_faviconico', 'wp_favicon_remover');
function wp_favicon_remover() {
    exit;
}
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/users/1/brand-marketing/web/ryokougyo-touroku.com/wp-content/themes/ryokougyo-touroku/functions.php:145) in <b>/home/users/1/brand-marketing/web/ryokougyo-touroku.com/wp-includes/pluggable.php</b> on line <b>1298</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/users/1/brand-marketing/web/ryokougyo-touroku.com/wp-content/themes/ryokougyo-touroku/functions.php:145) in <b>/home/users/1/brand-marketing/web/ryokougyo-touroku.com/wp-includes/pluggable.php</b> on line <b>1301</b><br />