Test and fix empty folders left behind during GC with the local filesystem storage driver

Problem

While working on !31 (merged) and !39 (merged), I noticed that when using the local filesystem driver, blobs and manifests deleted directly through their data/link full file path will cause their parent folders to be left behind empty.

Solution

Further testing is required to verify the impact of this. A viable solution is to delete the parent folder of a given data/link file after deleting the file itself. This can be achieved by customizing the DeleteFiles method for this specific driver.