legal-info: rename legal-warning-pkg-savednothing helper

legal-info: rename legal-warning-pkg-savednothing helper

This helper was called when none of the sources or license
files were saved.

Now we handle license files separately from the sources,
this is no longer the case: they are only called when the
sources are not saved.

Rename the handler and change the warning message accordingly.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>