Consider normative vs informative for term definitions

[alvestrand]

From Ben Campbell's IESG review:

Please consider whether the references to rtcweb-overview, RFC 4595, and
RFC 7656 should be normative references. They are cited for definition of
terms used in this document; if those definitions are needed to fully
understand this document, they should be normative. (IMHO, these are
borderline).

[alvestrand]

Earlier discussions have shown a preference for a) keeping terminology in -overview, and b) keeping references to -overview informational, to avoid the "all must be done before anything is done" problem.

Treating definitions consistently seems reasonable to me. Agree that it's borderline.
Advice sought.

[alvestrand]

After mulling on the matter, moving these to normative in -16.