doc: remove outdated s_client information in tls.md

There is a description of how to use s_client for testing of
renegotiation limits in the `tls` module documentation. The information
is somewhat out of scope, but it also may be somewhat problematic due to
changes/peculiarities (bugs?) in recent s_client. Remove the text.

Refs: #25381 (comment)

PR-URL: #25678
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

doc/api/tls.md

@@ -136,10 +136,6 @@ threshold is exceeded. The limits are configurable:
 The default renegotiation limits should not be modified without a full
 understanding of the implications and risks.
 
-To test the renegotiation limits on a server, connect to it using the OpenSSL
-command-line client (`openssl s_client -connect address:port`) then input
-`R<CR>` (i.e., the letter `R` followed by a carriage return) multiple times.
-
 ### Session Resumption
 
 Establishing a TLS session can be relatively slow. The process can be sped