Remove unnecessary memset after PR #2583 avoids accessing

the uninitialized session_id now.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2608)

ssl/ssl_sess.c

@@ -501,7 +501,6 @@ int ssl_get_prev_session(SSL *s, CLIENTHELLO_MSG *hello, int *al)
         SSL_SESSION data;
 
         data.ssl_version = s->version;
-        memset(data.session_id, 0, sizeof(data.session_id));
         memcpy(data.session_id, hello->session_id, hello->session_id_len);
         data.session_id_length = hello->session_id_len;