Comment 8 for bug 1778800

Observing unattended-upgrades/1.1ubuntu1.18.04.4 maintainer scripts show that the invoke-rc.d calls are indeed removed:

/var/lib/dpkg/info/unattended-upgrades.prerm:
...
# dh_installdeb will replace this with shell code automatically
# generated by other debhelper scripts.

exit 0
...

/var/lib/dpkg/info/unattended-upgrades.postinst:
...
# Automatically added by dh_installinit/11.1.6ubuntu2
if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ] || [ "$1" = "abort-deconfigure" ] || [ "$1" = "abort-remove
" ] ; then
        if [ -x "/etc/init.d/unattended-upgrades" ]; then
                update-rc.d unattended-upgrades defaults >/dev/null || exit 1
        fi
fi
# End automatically added section
...