Closing Rel-53

Rel 53 should be closed, since I have done
my action item without any problem.

Thanks,

Iwasa

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REL-53 Spec all feature Design Accepted Tom Rutt Iwasa
Title: Remove all mention of MessageId
Description: Folliwing the decisions made on closing issue REL-36, need to
ensure nothing remains of the old MessageId element or related concepts.
REL-52 is one example of an area where this is more complicated than an
editorial action item. This issue is an umbrella for any additional design
issues that come up from the (primarily editorial) removal of MessageId
mention. Priority may turn out to be Editorial.
Proposal: Let Iwasa take a crack at making this change as an editorial item
of work. If he runs into trouble, we will use this issue to discuss the
design issues.