C2MS13 — Remove fields in C2MS Messages that are duplicated between C2MS Messages and the Message Envelope

With the advent of the C2MS Message Envelope, some tracking or meta-data fields exist in both the new Message Envelope and in the already-existing C2MS Message. In 1.x, it is the case that we want to leave fields in the C2MS message and encourage migration toward Message Envelope usage. In a follow-on major release, assuming we make the Message Envelope required, the duplicated fields should be removed in the C2MS Message.