With the dependent change, zuul-sphinx will raise a warning when the
autoroles matcher finds a role without a README.rst. Since we
error-on-warnings this will stop the docs build. Thus we don't need
this explicit linters check.
Change-Id: I02eefce2448152505bacba3b2a12021515b4a31a
Depends-On: https://review.openstack.org/596014