quic: documentation and demo nits

quic: documentation and demo nits

The code for the quic demos (from the openssl guide) is presented as
modifications of tls-client-block.c.  Make it so that the quic code
better matches the tls code (drop unneeded assignments to "ret", use
the same comment on SSL_connect(), add the same printf() statement).

Also fix some minor typos.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22483)