Boy I wish! :|
When in private files, only by logging in as that Teacher can admin level actually see them - thus be able to delete via Admin UI.
Query
select contenthash,filearea,filename,filesize from `mdl_files` where
(`filearea` like "backup" and `filename` like "%.mbz%") order by
filesize DESC
Then manually remove the file in moodledata/filedir/contenthashdirs/contenthash/
and of course the row in DB mdl_files that referenced it.
Moosh does have a command: http://moosh-online.com/commands/
Example 4: Remove all automated backups and reclaim the space
moosh file-list -i 'component="backup" AND filearea="automated"' | moosh file-delete -s
moosh file-delete --flush
'spirit of sharing', Ken