Revert two Kernel changes that were causing test failures.

tests/language_2/assertion_initializer_const_error_test.dart

-// Copyright (c) 201, 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.
-// VMOptions=--assert_initializer
-
-class C {
-  static bool check(x, y) => x < y;
-  final int x;
-  const C(this.x);
-  // The expression is not a potentially constant expression.
-  // This is a compile-time error even in production mode.
-  const C.bc03(this.x, y)
-      : assert(check(x, y))  //# 01: compile-time error
-      ;
-}
-
-main() {
-  var c = new C.bc03(1, 2);
-  if (c.x != 1) throw "non-trivial use of c";
-}