CFC: remove "the actor's namespace" from section on Object IDs in ActivityPub spec

As noted in this issue, the section on object IDs in the ActivityPub spec
mentions creating URLs in "the actor's namespace" without defining what
that would mean:

https://github.com/w3c/activitypub/issues/443

To help with this problem, I've added the following proposed erratum:

Section 3.1, "Object identifiers", says in part that the server should
create an ID "in the actor's namespace". "The actor's namespace" is not
otherwise defined, making it impossible for implementers to comply. One
solution is to remove this term from the sentence: *However, for client to
server communication, a server receiving an object posted to the outbox
with no specified id SHOULD allocate an object ID and attach it to the
posted object.*

This is a call for consensus on adopting this erratum for ActivityPub. In
the absence of objections to this change by 12 Dec 2025 AOE EOD, I will add
this erratum to the Errata for ActivityPub, and make the corresponding
change to the editor's draft.

To comment, please comment on issue #443 or reply in this thread.

Thanks,

Evan