pkg-infra: DOWNLOAD is never called with two arguments

Currently, the DOWNLOAD helper accepts one or two arguments:
  - the source URI
  - the source filename; if missing, it is derived from the URI

But we have no caller of DOWNLOAD that passes a second argument.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>