Remove rpm list collection from RHN module

The RHN module duplicates RPM module functionality by collecting
a list of installed RPMs. Since the external satellite debugging
scripts also collect this it means the data is triplicated in an
sos report on satellite/spacewalk hosts.

Remove the duplication in RHN to lessen this somewhat.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>