[es8] Remove syntactic tail calls support.

test/message/syntactic-tail-call-in-comma.js

Index: test/message/syntactic-tail-call-in-comma.js
diff --git a/test/message/syntactic-tail-call-in-comma.js b/test/message/syntactic-tail-call-in-comma.js
deleted file mode 100644
index 402a4a8f7d9e83d4570ed7f22fe573c6501158e7..0000000000000000000000000000000000000000
--- a/test/message/syntactic-tail-call-in-comma.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// Copyright 2016 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --harmony-explicit-tailcalls
-"use strict";
-
-function f() {
-  return 1;
-}
-
-function g() {
-  return 1, 2, 3,   continue f() , 4  ;
-}