pkgset: Query Koji instead of PDC
    
    PDC is deprecated in upstream. The usecase for getting list of modules
    by NS, NSV or NSVC can however be satisfied by querying modules imported
    into Koji.
    
    This makes it possible to deprecate PDC configuration.
    
    Merges: https://pagure.io/pungi/pull-request/985
    Signed-off-by: Martin Curlej <mcurlej@redhat.com>