Remove nsis installer
    
    The only reason for us to keep maintaining the nsis installer was the
    activex plugin (spicex), which requires those nsis based installers.
    As the next release of RHEV/oVirt won't use the activex plugin (spicex)
    let's completely remove the nsis installer from our tree and focus on
    only maintain the msi installer.
    oVirt/RHEV is shipping virt-viewer based on 2.0 release and, if needed,
    they can stick to 3.0 branch in a future update (in case their plan goes
    wrong and they end up needing the nsis support).
    
    Related: rhbz#1324885 and rhbz#1316560
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Acked-by: Christophe Fergeau <cfergeau@redhat.com>