There were extraneous entries in the lists of signed key types:
these values describe the type of the key being signed (eg, ed25519
or RSA), not the type of the certificate.

Further, clarify Tor bug 40124, so that people know to expect
incorrect cert key types on older signing->link certs.

Signed-off-by: David Goulet <dgoulet@torproject.org>

Our docs accurately describe how to remove MAPADDRESS entries, but doesn't
demonstrate it. Exemplifying how to query our mappings and remove them.

  tpo/core/tor#40104

(tjr is okay with this)

It's under discussion on tor-dev.

We've talked about these, and in some cases begun to implement them.

They are implemented, and only need (possible) spec updates

Closes #30123

Thanks goes to Toke Høiland-Jørgensen.

Otherwise he suspsects that circuits will exit slow start too early.

We moved the fields to extrainto back in 0.2.0.x, which is now
long-obsolete -- it's time to move the description of the fields
there, and remove the legacy migration note.