Comment 4 for bug 1789469

to provide more context, seems that maas-rack-controller is being purged first:

Please, remove /var/spool/squid yourself.
Purging configuration files for bind9 (1:9.11.3+dfsg-1ubuntu1.2) ...
dpkg: warning: while removing bind9, directory '/var/cache/bind' not empty so not removed
dpkg: warning: while removing bind9, directory '/etc/bind' not empty so not removed
Purging configuration files for maas-region-controller (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...
Purging configuration files for maas-rack-controller (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...
nginx.service is a disabled or a static unit, not starting it.
dpkg: warning: while removing maas-rack-controller, directory '/var/log/maas/http' not empty so not removed
dpkg: warning: while removing maas-rack-controller, directory '/var/lib/maas/http' not empty so not removed
Purging configuration files for avahi-daemon (0.7-3.1ubuntu1.1) ...
rmdir: failed to remove '/var/run/avahi-daemon': Directory not empty
Purging configuration files for python3-twisted (17.9.0-2) ...
Purging configuration files for freeipmi-common (1.4.11-1.1ubuntu4.1) ...
Purging configuration files for isc-dhcp-server (4.3.5-3ubuntu7) ...
Purging configuration files for libvirt-clients (4.0.0-1ubuntu8.5) ...
dpkg: warning: while removing libvirt-clients, directory '/etc/libvirt' not empty so not removed
Purging configuration files for dbconfig-common (2.0.9) ...
dpkg: warning: while removing dbconfig-common, directory '/var/log/dbconfig-common' not empty so not removed
dpkg: warning: while removing dbconfig-common, directory '/etc/dbconfig-common' not empty so not removed
Purging configuration files for libipmiconsole2 (1.4.11-1.1ubuntu4.1) ...
Purging configuration files for maas-common (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...

This should stop all services