Unconditionally define session variable

Signed-off-by: Norbert Fabritius <norbert.fabritius@esrlabs.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 92e8add..8a76fbd 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -569,10 +569,8 @@
         psa_algorithm_t psk_hash_alg;
         int allowed_key_exchange_modes;
 
-#if defined(MBEDTLS_SSL_SESSION_TICKETS)
         mbedtls_ssl_session session;
         mbedtls_ssl_session_init(&session);
-#endif
 
         MBEDTLS_SSL_CHK_BUF_READ_PTR(p_identity_len, identities_end, 2 + 1 + 4);
         identity_len = MBEDTLS_GET_UINT16_BE(p_identity_len, 0);