We only ever use these for passing them into Endpoint construction. Let's remove them. Removing them also shows that the corresponding field in Endpoint is essentially read-only, so we can completely avoid passing in protocol IDs to Endpoint.
Created attachment 8890530 [details] [diff] [review] remove unused *MsgStartChild constants
Pushed by firstname.lastname@example.org: https://hg.mozilla.org/integration/mozilla-inbound/rev/f682a94b7474 remove unused *MsgStartChild constants; r=billm