Don't remove sessions from the cache during PHA in TLSv1.3

If we issue new tickets due to post-handshake authentication there is no
reason to remove previous tickets from the cache. The code that did that
only removed the last session anyway - so if more than one ticket got
issued then those other tickets are still valid.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6722)

ssl/statem/statem_srvr.c

@@ -3648,8 +3648,6 @@ MSG_PROCESS_RETURN tls_process_client_certificate(SSL *s, PACKET *pkt)
      */
 
     if (s->post_handshake_auth == SSL_PHA_REQUESTED) {
-        int m = s->session_ctx->session_cache_mode;
-
         if ((new_sess = ssl_session_dup(s->session, 0)) == 0) {
             SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                      SSL_F_TLS_PROCESS_CLIENT_CERTIFICATE,
@@ -3657,13 +3655,6 @@ MSG_PROCESS_RETURN tls_process_client_certificate(SSL *s, PACKET *pkt)
             goto err;
         }
 
-        if (m & SSL_SESS_CACHE_SERVER) {
-            /*
-             * Remove the old session from the cache. We carry on if this fails
-             */
-            SSL_CTX_remove_session(s->session_ctx, s->session);
-        }
-
         SSL_SESSION_free(s->session);
         s->session = new_sess;
     }