This module contains bits that are either unused (the Rhsm* classes), or
used only by deprecated modules (the RegistrationBase class).
Considering that the bits here have not seen updates in years, it is
unlikely that anyone is actually using them as "library".
Hence, deprecate the whole module altogether:
- the Rhsm* classes, as not used by anything, are slated for removal in
9.0.0
- the RegistrationBase class is slated for removal in 10.0.0, together
with its only user (i.e. the rhn_register module)
