Remove KEEP_FILE implementation

Closes #46 (closed)

We believe we needed this for the alma-apbatch project due to the nature of the s3 bucket in use being a reflection of a more complicated samba network drive. In that case, we were worried about subpaths disappearing and throwing errors due to the samba mount. But that shouldn't be an issue with this application.

Note: Instead of completely removing the keep file test, I marked it pending and added some TODO notes. I'm thinking that test setup is probably a good starting point for adding tests when we implement #43 (closed)