Remove all snapshots from Duplicacy storage

As backups are refactored, I like to tidy up and remove those I don’t need. It avoids the confusion of duplicates. Since Duplicacy can keep multiple backups in a single storage location, I need to remove all instances of a snapshot.

Using the Duplicacy web interface,

1. Disable/delete any backups writing to the storage for the snapshot id
2. Create a Prune job, for the correct storage
3. Run with options -id <the-snapshot-id> -all -exclusive -exhaustiveto remove all revisions and mark unreferenced chunks as fossils.
4. Panic because you think you’ve got it wrong 🤣
5. Run with options -id <the-snapshot-id> -all -exclusive -delete-only to delete the fossil chunks.
6. Delete the empty snapshot directory. It will contain metadata files (one number for each previous snapshot and these are ok to delete)
7. Repeat for the offsite copy.