legal-info: remove outdated comment

legal-info: remove outdated comment

This comment is outdated since the assignment of $(2)_MANIFEST_TARBALL
and $(2)_MANIFEST_SITE have been removed, which happened in
b9f4727ff4d512868352494f5209fff4da147473.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Thomas: adjust comment as suggested by Yann E. MORIN.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>