Remove the plugin OTOBO::XML::WADL::XSDValidator
This is a policy for Web Application Description Language. As far as I see, e.g. in development/webservices/ , there currently is no support for WADL in OTOBO core. Also, WADL seem to be dead, at least I have never heard about it and I could not find recent news about it. See also https://news.ycombinator.com/item?id=28401885 .
So, let's consider it as cruft and remove it.