drop some no-longer-relevant TODO(TLS1.3) entries

We prevent compression both when the server is parsing the ClientHello
and when the client is constructing the ClientHello.  A 1.3 ServerHello
has no way to hand us back a compression method, and we already check
that the server does not try to give us back a compression method that
we did not request, so these checks seem sufficient.

Weaken the INSTALL note slightly, as we do now expect to interoperate
with other implementations.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3131)