Re-enable TLSv1.3 session resumption related tests in sslapitest

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2259)

test/sslapitest.c

@@ -789,12 +789,6 @@ static int execute_test_session(SSL_SESSION_TEST_FIXTURE fix)
     SSL_CTX_set_min_proto_version(cctx, TLS1_2_VERSION);
 #endif
 
-    /*
-     * TODO(TLS1.3): Test temporarily disabled for TLS1.3 until we've
-     * implemented session resumption.
-     */
-    SSL_CTX_set_max_proto_version(cctx, TLS1_2_VERSION);
-
     /* Set up session cache */
     if (fix.use_ext_cache) {
         SSL_CTX_sess_set_new_cb(cctx, new_session_cb);