More directive documentation on how to delete packets

[jeffeaton]

The current description about deleting packets from the archive is helpful articulation about the issues that can arise from changes to the archive and what to when archive becomes out of sync. But it also makes the user a bit nervous about messing with things in the archive.

I think it would be helpful to start this section concise directive instructions about the appropriate steps to take to (intentionally) delete something from the archive (e.g. "1. delete the folder from archive/<report>/<packet_id>; 2. run orderly_validate_archive()", or whatever correct steps may be), and then give the full explanation about the concerns about archive becoming out of sync.