Update Storage.RemoveAll() and Storage.RemoveAllButCurrent() to return
the details about the deleted items. This helps emit useful information
about garbage collection in the controllers and ignore no-op garbage
collections.
RemoveAll() returns the path of the deleted directory if any.
RemoveAllButCurrent() returns a slice of path of all the deleted items
from a resource's artifact dir.
Signed-off-by: Sunny <darkowlzz@protonmail.com>