Remove --harmony-async-await runtime flag

test/debugger/debug/harmony/async-debug-step-next-constant.js

-// Copyright 2016 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-async-await
-
-var Debug = debug.Debug;
-var step_count = 0;
-
-function listener(event, execState, eventData, data) {
-  if (event != Debug.DebugEvent.Break) return;
-  try {
-    var line = execState.frame(0).sourceLineText();
-    print(line);
-    var [match, expected_count, step] = /\/\/ B(\d) (\w+)$/.exec(line);
-    assertEquals(step_count++, parseInt(expected_count));
-    if (step != "Continue") execState.prepareStep(Debug.StepAction[step]);
-  } catch (e) {
-    print(e, e.stack);
-    quit(1);
-  }
-}
-
-Debug.setListener(listener);
-
-async function f() {
-  var a = 1;
-  debugger;          // B0 StepNext
-  a +=               // B1 StepNext
-       await         // B3 StepNext
-             5;      // B2 StepNext
-  return a;          // B4 StepNext
-}                    // B5 Continue
-
-f();
-
-%RunMicrotasks();
-
-assertEquals(6, step_count);