[turbofan] Disable usage of {maybe_assigned} variable flag.

test/mjsunit/regress/regress-crbug-659915b.js

+// 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: --allow-natives-syntax --min-preparse-length=10
+
+(function() {
+  var x = 23;
+  function f() { return x; }
+  function g() { [x] = [x + 1]; }
+  function h() { g(); return x; }
+
+  function boom() { return h() }
+
+  assertEquals(24, boom());
+  assertEquals(25, boom());
+  assertEquals(26, boom());
+  %OptimizeFunctionOnNextCall(boom);
+  assertEquals(27, boom());
+})();