[FAB-1700] Determinsitic BlockData hashing

https://jira.hyperledger.org/browse/FAB-1700

This is a companion item to

https://jira.hyperledger.org/browse/FAB-1699

It removes the protobuf serialization of the BlockData in favor a simple
concatenation of the byte contents.  Eventually, this should be encoded
as a Merkle tree at the configured width, but, like with our hashing
algorithm, for v1, we will make it configurable at a later date, see:

https://jira.hyperledger.org/browse/FAB-1983



Change-Id: I8a09e84f1c35d8fe1269339a443c44ba01b841a8
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>