Remove pre-Lithium serialization support in sal-distributed-datastore

Remove pre-Lithium serialization support in sal-distributed-datastore

We've had 3 releases since Helium so it should be safe to remove the
backwards compatible serialization support for the old format utilized by
NormalizedNodeToNodeCodec. It's not likely any user would have persisted
data in the old format in production (mainly b/c clustering was essentially
beta at best) but, in Boron, persisted journals will get snapshotted anyway
in the post-Helium format due to message migration.

Change-Id: I3fba07748b798962b7816878a791cf50a97e5a50
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>