Remove unreachable statement.

The return at the end isn't reachable.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5442)

ssl/statem/statem_srvr.c

@@ -1150,7 +1150,6 @@ WORK_STATE ossl_statem_server_post_process_message(SSL *s, WORK_STATE wst)
     case TLS_ST_SR_KEY_EXCH:
         return tls_post_process_client_key_exchange(s, wst);
     }
-    return WORK_FINISHED_CONTINUE;
 }
 
 #ifndef OPENSSL_NO_SRP