Remove TLS1.3 TODO around testing for session id length

TLSv1.3 will do the same thing as TLSv1.2 with tickets with regards to session
ids, i.e. it will create a synthetic session id when the session is established,
so it is reasonable to check the session id length, even in TLSv1.3.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3008)

ssl/statem/statem_clnt.c

@@ -2442,7 +2442,6 @@ MSG_PROCESS_RETURN tls_process_new_session_ticket(SSL *s, PACKET *pkt)
     if (ticklen == 0)
         return MSG_PROCESS_CONTINUE_READING;
 
-    /* TODO(TLS1.3): Is this a suitable test for TLS1.3? */
     if (s->session->session_id_length > 0) {
         int i = s->session_ctx->session_cache_mode;
         SSL_SESSION *new_sess;