Remove nemo-extension-xreader, obsoleted by xreader (#1609294)
    
    Per @robatino, xreader in stable updates for F27 and F28 and in
    Rawhide obsoletes nemo-extension-xreader, but because of this
    comps entry, `dnf groupinstall cinnamon-desktop` tries to pull
    in the nemo-extension-xreader package and an old xreader. Let's
    take it out.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>