Remove support for legacy const, part 1

test/mjsunit/es6/block-let-contextual-sloppy.js

 // Copyright 2015 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-sloppy --harmony-sloppy-let --legacy-const
+// Flags: --harmony-sloppy --harmony-sloppy-let
 
-// let is usable as a variable with var or legacy const, not let or ES6 const
+// let is usable as a variable with var, but not let or ES6 const
 
 (function (){
   assertEquals(undefined, let);
 
   var let;
 
   let = 5;
   assertEquals(5, let);
 
   (function() { var let = 1; assertEquals(1, let); })();
@@ skipping 24 matching lines @@
 
 assertThrows(function() { return let; }, ReferenceError);
 
 (function () {
   let obj = {};
   var {let} = {let() { return obj; }};
   let().x = 1;
   assertEquals(1, obj.x);
 })();
 
-(function () {
-  let obj = {};
-  const [let] = [function() { return obj; }];
-  let().x = 1;
-  assertEquals(1, obj.x);
-})();
-
 (function() {
   function let() {
     return 1;
   }
   assertEquals(1, let());
 })()
 
 assertThrows('for (let of []) {}', SyntaxError);