Dealing with pubrules and Gregg's editor status

[afs]

See w3c/rdf-concepts#247

the W3C automated process requires all editors to be active W3C members;
we discussed with the chairs and other co-editors and this solution was proposed.

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[afs]

@Tpt - this PR is one of several updating the editors section of syntax documents.

We don't have a editor for RDF/XML at the moment. (I'm not sure the document will auto-publish after this PR is merged.)

Could I ask for a review from a knowledgeable working group member to verify this PR follows proper process? (forgot you are not available ATM)

Thanks.