delete_empty_dirs() task name misleading.

[danmarsden]

The delete_empty_dirs() task doesn't just delete empty directories - it also deletes files that are not included in the files table (which is probably a good thing, just not what we expected to see when running the task.)

We should update the title of this task to make it clear that it's not just deleting empty dirs - It would also be nice to include some better output in the task to state if it's deleted any files along with the empty dirs...