debian/docs: don't explicitly install NEWS

dh_installchangelogs does that automatically.

Refs T770. Similar to D1439.

Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D1644

debian/docs

-NEWS
 README
 TODO