stable/viewporter: remove wp_viewport.set request

Remove the old, redundant request. The new way is to call both
wp_viewport.set_source and wp_viewport.set_destination when you want to
set everything.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Acked-by: Bryce Harrington <bryce@osg.samsung.com>