Don't list grub2-efi for live images
    
    The arch-specific sub-packages that provide grub2-efi on each
    arch are listed in @anaconda-tools comps group anyway (so this
    is redundant), and requiring it by name in a kickstart causes
    i686 live image composes to fail because it is no longer built
    for i686.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>