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>