Revert two Kernel changes that were causing test failures.

tests/language_strong/async_call_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:async";
 import "package:expect/expect.dart";
 
 var result = "";
 
 foo() {
   result += "foo";
 }
 
 bar() async {
   result += "bar";
 }
 
 main() async {
   var f = new Future(foo);
   var b = bar();
   Expect.equals("", result);
   scheduleMicrotask(() => result += "micro");
   await b;
   await f;
 
   // Validates that bar is scheduled as a microtask, before foo.
   Expect.equals("barmicrofoo", result);
 }