Delete dart_backend from compiler.

tests/compiler/dart2js/platform_consistency_test.dart

 // Copyright (c) 2015, the Fletch 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.md file.
 
 import "package:compiler/src/platform_configuration.dart";
 import "package:compiler/src/source_file_provider.dart";
 import "package:compiler/compiler_new.dart";
 import "package:expect/expect.dart";
 
 Uri unsupported =  Uri.parse("unsupported:");
 
 main() async {
   CompilerInput input = new CompilerSourceFileProvider();
   Map<String, Uri> client = await load(
       Uri.base.resolve("sdk/lib/dart_client.platform"),
       input);
   Map<String, Uri> server = await load(
       Uri.base.resolve("sdk/lib/dart_server.platform"),
       input);
   Map<String, Uri> shared = await load(
       Uri.base.resolve("sdk/lib/dart_shared.platform"),
       input);
-  Map<String, Uri> dart2dart = await load(
-      Uri.base.resolve("sdk/lib/dart2dart.platform"),
-      input);
   Expect.setEquals(new Set.from(shared.keys), new Set.from(client.keys));
   Expect.setEquals(new Set.from(shared.keys), new Set.from(server.keys));
-  Expect.setEquals(new Set.from(shared.keys), new Set.from(dart2dart.keys));
 
   for (String libraryName in shared.keys) {
     test(Map<String, Uri> m) {
       if (m[libraryName] != unsupported &&
           shared[libraryName] != unsupported) {
         Expect.equals(shared[libraryName], m[libraryName]);
       }
     }
     test(client);
     test(server);
-    test(dart2dart);
   }
  }