Remove always-on --harmony-rest-parameters flag

test/mjsunit/es6/arrow-rest-params-lazy-parsing.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-rest-parameters
 // Flags: --min-preparse-length=0
 
 (function testRestIndex() {
   assertEquals(5, ((...args) => args.length)(1,2,3,4,5));
   assertEquals(4, ((a, ...args) => args.length)(1,2,3,4,5));
   assertEquals(3, ((a, b, ...args) => args.length)(1,2,3,4,5));
   assertEquals(2, ((a, b, c, ...args) => args.length)(1,2,3,4,5));
   assertEquals(1, ((a, b, c, d, ...args) => args.length)(1,2,3,4,5));
   assertEquals(0, ((a, b, c, d, e, ...args) => args.length)(1,2,3,4,5));
 })();
@@ skipping 120 matching lines @@
 })();
 
 
 (function testUnmappedArguments() {
   // Normal functions make their arguments object unmapped, but arrow
   // functions don't have an arguments object anyway.  Check that the
   // right thing happens for arguments in arrow functions with rest
   // parameters.
   assertSame(arguments, ((...rest) => arguments)());
 })();