Detecting tar files then falling back for calculating digests turned out to be
fairly unreliable. Likely, the implementation was broken for content that was
not a tarfile. Also, for the use case of the registry, it is really not needed.
This functionality has been removed in FromReader and FromBytes. FromTarArchive
has been added for convenience.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
10a4605ec2