Remove download manager wish list

The website currently has a page of "requirements" for Newport, the
download manager. This page lists a number of recommendations for
requirements were drawn up after the initial implementation and review of
Newport. Looking at the commit history for Newport, it seems that these
requirements have never been implemented. Newport is not widely used and
is part of the legacy application framework and thus isn't receiving any
development effort.

As this page doesn't reflect the reality of what's available or likely to be
available in Apertis, delete it.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>