Update several URLs pointing to https://www.debian.org/doc/debian-policy to match the new URLs since debian-policy 4.1.0.

This is work in progress, this commit changes:

sed "s|https://www.debian.org/doc/debian-policy/#details-of-unpack-phase-of-installation-or-upgrade|https://www.debian.org/doc/debian-policy/ch-maintainerscripts.html#details-of-unpack-phase-of-installation-or-upgrade|g

"

Signed-off-by: Holger Levsen <holger@layer-acht.org>