MQTT: WIP, subscibed topics have no "Retained" attribute.
Allow subscribed and published data models to be different, by removing "Retained" column.
<xsd:element name="Xenomai">
<xsd:complexType>
%(toolchain_gcc)s
<xsd:attribute name="XenoConfig" type="xsd:string" use="optional" default="xeno-config"/>
</xsd:complexType>
</xsd:element>