[webauthn] Merged Pull Request: Tone back trust assumption in authn ceremony structures section

emlun has just merged emlun's pull request 960 for https://github.com/w3c/webauthn:

== Tone back trust assumption in authn ceremony structures section ==
This would merge into #956.

See https://github.com/w3c/webauthn/pull/842#discussion_r195887194 and https://github.com/w3c/webauthn/pull/899#discussion_r195171633


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See https://github.com/w3c/webauthn/pull/960