If you ever find yourself confronted with a Plesk system that is running out of disk space, and you just want to get rid off all the misconfigured „keep forever“ backups, here’s how to remove them all from the command line:
/usr/local/psa/admin/bin/pmm-ras --get-dump-list | egrep "name=\".*.xml" | awk -F '"' '{ print $2 }' | xargs -I {} /usr/local/psa/admin/bin/pmm-ras --verbose --debug --delete-dump --dump-specification={} --session-path=/var/log/plesk/PMM