Remove runtime flags for sloppy mode block scoping features

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
-
 // 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);
 
@@ skipping 33 matching lines @@
 })();
 
 (function() {
   function let() {
     return 1;
   }
   assertEquals(1, let());
 })()
 
 assertThrows('for (let of []) {}', SyntaxError);