Removes dartc reliance on its own libraries, now can be targeted at any implementation's libraries

compiler/lib/implementation/time_zone_implementation.dart

-// Copyright (c) 2011, 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.
-
-// Dart core library.
-
-// JavaScript implementation of TimeZoneImplementation.
-class TimeZoneImplementation implements TimeZone {
-  const TimeZoneImplementation.utc() : this.isUtc = true;
-  const TimeZoneImplementation.local() : this.isUtc = false;
-
-  bool operator ==(other) {
-    if (!(other is TimeZoneImplementation)) return false;
-    return isUtc == other.isUtc;
-  }
-
-  String toString() {
-    if (isUtc) return "TimeZone (UTC)";
-    return "TimeZone (Local)";
-  }
-
-  final bool isUtc;
-}