Update TLS usage.

[markafoltz]

This PR addresses editorial issues #219 and #220, that were resolved to remove profile- and extension-specific information from the usage of TLS 1.3. Two parameters are retained that identify an incoming TLS connection request as intended for a specific OSP Agent.

Cipher and signature algorithm recommendations will likely be added back to this section in a later PR to close Issue #218.

---

Preview | Diff

[markafoltz]

PTAL @tidoust.

Also, FYI @DavidSchinazi and @pwnall as this was based on your feedback from TPAC 2019 (thank you!):
https://www.w3.org/2019/09/15-webscreens-minutes.html#x05

[DavidSchinazi]

Thanks!

[tidoust]

I don't know much about TLS 1.3 internals so cannot comment on whether something might be missing, but this looks good to me and aligned with what the group discussed and resolved.