vnc: replace hweight_long() with ctpopl()

ctpopl() has a better implementation than hweight_long() and ui/vnc.c
being the last user of hweight_long(), we can simply remove it.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1489415605-13105-1-git-send-email-clg@kaod.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>