Enable ES6 Map and Set by default

test/mjsunit/es6/mirror-collections.js

 // Copyright 2014 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: --expose-debug-as debug --expose-gc --harmony-collections
+// Flags: --expose-debug-as debug --expose-gc
 
 function testMapMirror(mirror) {
   // Create JSON representation.
   var serializer = debug.MakeMirrorSerializer();
   var json = JSON.stringify(serializer.serializeValue(mirror));
 
   // Check the mirror hierachy.
   assertTrue(mirror instanceof debug.Mirror);
   assertTrue(mirror instanceof debug.ValueMirror);
   assertTrue(mirror instanceof debug.ObjectMirror);
@@ skipping 119 matching lines @@
       found++;
     }
     if (Object.is(values[i], o3)) {
       found++;
     }
   }
   assertEquals(2, found);
 }
 
 testWeakSetValues(weakSetMirror);