revert obsolete, as %python_provide does it (undocumented)
    
    kparal pointed out python2-libsolv was already obsoleting
    python-libsolv, even though this wasn't written in the spec.
    This puzzled us, but I found out today that the python_provide
    macro actually also produces an Obsoletes: line, but this is
    not documented anywhere besides the trac ticket:
    https://fedorahosted.org/fpc/ticket/565
    so we actually didn't need to add the Obsoletes: directly.
    This reverts to the spec as of -3.