MQTT: remove standalone MQTT clien generator code.
Code was inherited from OPC-UA extension, but not properly maintained.
<?xml version='1.0' encoding='utf-8'?>
<MQTTClient xmlns:xsd="http://www.w3.org/2001/XMLSchema" Broker_URI="wss://192.168.19.25:18885">
<AuthType>
<x509 Client_certificate="" Broker_certificate="test-root-ca.crt" Verify_hostname="false"/>
</AuthType>
</MQTTClient>