Remove XMPP

... most likely it will not come back soon

contact.html

@@ -14,7 +14,6 @@ title: Contact
 <ul>
     <li><a href="https://matrix.to/#/@kunsi:franzi.business">@kunsi:franzi.business [Matrix]</a></li>
     <li>K9BC697E [Threema]</li>
-    <li><a href="xmpp:franzi@kunsmann.eu">franzi@kunsmann.eu [XMPP]</a></li>
     <li>Telegram</li>
     <li>WhatsApp</li>
 </ul>