Move i686 F31+ filter, drop ppc64 F29+ one
    
    We previously did a filter like the one for 'i686 on F31+' for
    'ppc64 on F29+', only in a different place which was actually a
    better place. That filter is now unneeded as F28 went EOL, so
    drop it...but move the i686 F31+ filter into the same place, as
    it's better done there than in create().
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>