Following alexey-tikhonov's suggestion.
Since we've dropped the 'owner' field in the data returned for
get_subid_ranges, we can just return a single allocated array of
simple structs. This means we can return a ** instead of ***, and
we can get rid of the subid_free_ranges() helper, since the caller
can just free() the returned data.
Signed-off-by: Serge Hallyn <serge@hallyn.com>