[es6] Remove harmony-classes flag

test/mjsunit/harmony/debug-step-into-class-extends.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 --harmony-classes
-
-'use strict';
-
-var Debug = debug.Debug
-
-var done = false;
-var stepCount = 0;
-
-function listener(event, execState, eventData, data) {
-  if (event == Debug.DebugEvent.Break) {
-    if (!done) {
-      execState.prepareStep(Debug.StepAction.StepInto);
-      var s = execState.frame().sourceLineText();
-      assertTrue(s.indexOf('// ' + stepCount + '.') !== -1);
-      stepCount++;
-    }
-  }
-};
-
-Debug.setListener(listener);
-
-function GetBase() {
-  var x = 1;   // 1.
-  var y = 2;   // 2.
-  done = true; // 3.
-  return null;
-}
-
-function f() {
-  class Derived extends GetBase() {} // 0.
-}
-
-var bp = Debug.setBreakPoint(f, 0);
-f();
-assertEquals(4, stepCount);
-
-Debug.setListener(null);