[es8] Remove syntactic tail calls support.

test/message/syntactic-tail-call-of-identifier.js

Index: test/message/syntactic-tail-call-of-identifier.js
diff --git a/test/message/syntactic-tail-call-of-identifier.js b/test/message/syntactic-tail-call-of-identifier.js
deleted file mode 100644
index b3ca31df01996114604d7b59e10ce6448131ca7a..0000000000000000000000000000000000000000
--- a/test/message/syntactic-tail-call-of-identifier.js
+++ /dev/null
@@ -1,10 +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 g(x) {
-  return continue   x  ;
-}