package/pkg-download: do not hard-code QUIET

Do not hard-code QUIET in our download commands, since it is handled in
the backends.

Suggested by Fabio.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>