Remove server hostname from mail account configuration info

Now that per-domain mail servers are properly supported, clients should not be instructed to use the server host name but mail.domain.tld instead.

web/templates/admin/edit_mail_acc.html

@@ -155,7 +155,6 @@
                         <tr>
                             <td colspan="2">
                                 <select id="mail_configuration" class="vst-list flat">
-                                    <option v_type="hostname" domain="<?=$hostname?>"><?=__('Use server hostname')?></option>
                                     <option v_type="hostname" domain="<?=$v_domain?>"><?=__('Use domain hostname')?></option>
                                     <option v_type="starttls"><?=__('Use STARTTLS')?></option>
                                     <option v_type="ssl"><?=__('Use SSL / TLS')?></option>