revert occasionally committed changed first_steps project.
project was changed by commit:
update translations from https://www.transifex.com/beremiz/beremiz-ide (756d02cf78db)
<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>