Resolution: Not a Bug
Let's have an application that uses just resteasy-client (not server!)
None of its dependencies should declare @WebServlet
resteasy-jaxrs declares (since 3.0.20.Final) org.jboss.resteasy.plugins.server.servlet.HttpServlet30Dispatcher as a @WebServlet
Why is it a problem?
a) Because this global servlet conflicts with some frameworks e.g. Spring MVC
b) it's unexpected that applying a CLIENT library causes registration of SERVLET which is by it nature server-side.
A partial workaround exists:
metadata-complete="true" in web.xml
(but it may influence a lot of other technologies)