disable xmlrpc voucher sync, current code is defective and seems pretty unsafe

src/www/services_captiveportal_vouchers.php

@@ -608,6 +608,7 @@ function enable_change(enable_change) {
 														 
 													</td>
 												</tr>
+<!-- voucher xmlrpc, disabled 												
 												<tr>
 													<td colspan="2" valign="top" class="listtopic"><?=gettext("Voucher database synchronization"); ?></td>
 												</tr>
@@ -640,6 +641,7 @@ function enable_change(enable_change) {
 														<br /><?=gettext("This is the password of the master voucher nodes webConfigurator."); ?>
 													</td>
 												</tr>
+-->												
 												<tr>
 													<td width="22%" valign="top">&nbsp;</td>
 													<td width="78%">