Remove wget + rpm workaround to manage repos install in CentOS

RDO has moved rdo-release packages to a new infra which supports EMS so
we do not need to wget it and install it using local rpm install.

This partially reverts [1].

[1] https://review.opendev.org/c/openstack/devstack/+/884277/

Change-Id: I189d0c3da0e7b017e2568022c14e6c8fb28251f1
1 file changed