migrated-from-my.cnf-settings.conf is not removed upon package purge

Upon package installation, postinst script creates migrated-from-my.cnf-settings.conf file and puts it into /etc/systemd/system/mariadb.service.d/. This file doesn't appear to belong to any package, so it doesn't get removed upon full apt-get remove ... or purge, and thus neither is the whole /etc/systemd/system/mariadb.service.d folder.

Note: I'm pretty sure previous versions are also affected, but I didn't check, thus only 10.4 in the 'Affected' field.