MQTT: remove standalone MQTT clien generator code.
Code was inherited from OPC-UA extension, but not properly maintained.
# opcua/__init__.py
from .client import OPCUAClient
# class RootClass(object):
# XSD = """<?xml version="1.0" encoding="ISO-8859-1" ?>
# <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
# </xsd:schema>
# """
# CTNChildrenTypes = [("OPCUAClient", OPCUAClient, "OPCUA Client")]
#