Drop grub2 prelink configuration
    
    A /etc/prelink.conf.d/grub2.conf is shipped to avoid SELinux to warn about
    security violations when SELinux is enforced and allow_execstack is off.
    
    But the tools have been fixed a long time ago and the allow list shouldn't
    be needed anymore, let's just drop it.
    
    Resolves: rhbz#1659675
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>