deb: update debhelper compat level to 13

[thaJeztah]

• depends on deb: remove ubuntu 20.04 "focal", as it reached EOL #1200
• relates to [master] Update "deb" packaging to use "dh_installsystemd", and remove upstart script #914
• relates to [master] Update "deb" packaging to use "dh_installsystemd" #686

Now that Ubuntu 20.04 and Debian 10 "buster" are removed, we no longer need to stay on level 12, and can remove the override_dh_dwz that was added in f9ac2f6 / 5c01d5b

This also removes the now-obsolete upstart script and updates the
"debhelper compat level" to 12 (which necessitates adding "override_dh_dwz"
-- safe to remove once we can update to debhelper-compat 13+).

(See also https://lists.debian.org/debian-devel-announce/2020/02/msg00000.html)

- What I did

- How I did it

- How to verify it

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Interesting;

setuptool.sh
# TODO: how can we install vpnkit?
make[1]: Leaving directory '/root/build-deb'
   debian/rules override_dh_install
make[1]: Entering directory '/root/build-deb'
dh_install
# TODO Can we do this from within our container?
dh_apparmor --profile-name=docker-ce -pdocker-ce
make[1]: Leaving directory '/root/build-deb'
   dh_installdocs
   dh_installchangelogs
   dh_installman
   debian/rules override_dh_installinit
make[1]: Entering directory '/root/build-deb'
# use "docker" as our service name, not "docker-ce"
dh_installinit --name=docker
make[1]: Leaving directory '/root/build-deb'
   debian/rules override_dh_installsystemd
make[1]: Entering directory '/root/build-deb'
# use "docker" as our service name, not "docker-ce"
dh_installsystemd --name=docker
make[1]: Leaving directory '/root/build-deb'
   dh_perl
   dh_link
   dh_strip_nondeterminism
   dh_compress
   dh_fixperms
   dh_missing
   dh_dwz -a
dwz: debian/docker-ce-rootless-extras/usr/bin/rootlesskit: Found compressed .debug_aranges section, not attempting dwz compression
dh_dwz: error: dwz -- debian/docker-ce-rootless-extras/usr/bin/rootlesskit returned exit code 1
dwz: debian/docker-compose-plugin/usr/libexec/docker/cli-plugins/docker-compose: .debug_info section not present
dwz: debian/docker-model-plugin/usr/libexec/docker/cli-plugins/docker-model: .debug_info section not present
dwz: debian/docker-ce/usr/bin/docker-proxy: .debug_info section not present
dwz: debian/docker-ce/usr/bin/dockerd: Found compressed .debug_aranges section, not attempting dwz compression
dwz: debian/docker-ce/usr/libexec/docker/docker-init: .debug_info section not present
dwz: Too few files for multifile optimization
dh_dwz: error: dwz -mdebian/docker-ce/usr/lib/debug/.dwz/x86_64-linux-gnu/docker-ce.debug -M/usr/lib/debug/.dwz/x86_64-linux-gnu/docker-ce.debug -- debian/docker-ce/usr/bin/docker-proxy debian/docker-ce/usr/bin/dockerd debian/docker-ce/usr/libexec/docker/docker-init returned exit code 1
dh_dwz: error: Aborting due to earlier error
make: *** [debian/rules:162: binary] Error 25
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2
make[1]: *** [Makefile:90: debian-bookworm] Error 2
make[1]: Leaving directory '/home/runner/work/docker-ce-packaging/docker-ce-packaging/deb'
make: *** [Makefile:91: debian-bookworm] Error 2
Error: Process completed with exit code 2.