libvirt.spec: Don't expect virt-admin in libvirt-admin yet
    
    While Martin introduced the binary (and its manpage) in commit
    4e7ccf87133 it was pushed by mistake. Therefore it was reverted in
    220393bfb043. The problem is, the original commit was not quite right
    as the binary was added into the spec file in a different commit:
    55e0c840af. So as long as the binary does not exist, we must remove it
    from the spec file too.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>