IANA requests seem to be incorrect for a -bis

[tfpauly]

The current IANA Considerations for H2 bis has several requests to IANA that seem to be appropriate for the original document, but not a bis now that the registries are already filled out. Shouldn't these be reworded to say "this document updates..." or explain that the references for registries should point to this document, rather than the old RFC?

This document establishes a registry for HTTP/2 frame type codes.