Implement S3 object/directory deletion
Implement S3 object/directory deletion

There are two ObjectManager APIs:

- delete_file
- delete_directory

The delete_directory method uses a more efficient bulk API. There should
probably also be a delete_files method to do the same, but for files in
general.

For DM-4196.

lsst-sqre/ltd-mason,lsst-sqre/ltd-mason