Revise s_client and s_server verbiage re secure renegotiation.

Revise s_client and s_server verbiage re secure renegotiation.

Since TLS v1.3 eschews renegotiation entirely it’s misleading to have
these apps say it’s “not supported” when in fact the TLS version is
new enough not to need renegotiation at all.

Reviewed-by: Ben Kaduk <kaduk@mit.edu>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16937)