Use xml.resource.org bibxml in the oggopus draft.

These aren't available over https, but actually work, unlike
the old reference urls.

doc/draft-ietf-codec-oggopus.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE rfc SYSTEM 'rfc2629.dtd' [
-<!ENTITY rfc2119 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.2119.xml'>
-<!ENTITY rfc3533 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.3533.xml'>
-<!ENTITY rfc3629 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.3629.xml'>
-<!ENTITY rfc4732 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.4732.xml'>
-<!ENTITY rfc5334 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.5334.xml'>
-<!ENTITY rfc6381 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.6381.xml'>
-<!ENTITY rfc6716 PUBLIC '' 'https://xml2rfc.tools.ietf.org/tools/xml2rfc/public/rfc/bibxml/reference.RFC.6716.xml'>
+<!ENTITY rfc2119 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'>
+<!ENTITY rfc3533 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3533.xml'>
+<!ENTITY rfc3629 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3629.xml'>
+<!ENTITY rfc4732 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4732.xml'>
+<!ENTITY rfc5334 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5334.xml'>
+<!ENTITY rfc6381 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6381.xml'>
+<!ENTITY rfc6716 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6716.xml'>
 ]>
 <?rfc toc="yes" symrefs="yes" ?>