Move kernel baseline tests to front_end.

pkg/front_end/test/fasta/rasta/duplicated_mixin.dart

Index: pkg/front_end/test/fasta/rasta/duplicated_mixin.dart
diff --git a/pkg/front_end/test/fasta/rasta/duplicated_mixin.dart b/pkg/front_end/test/fasta/rasta/duplicated_mixin.dart
deleted file mode 100644
index 08368cfe449dab0e4c25587c302575b44ea83f57..0000000000000000000000000000000000000000
--- a/pkg/front_end/test/fasta/rasta/duplicated_mixin.dart
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright (c) 2016, 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.md file.
-
-class Mixin {
-  var field;
-}
-
-class A extends Object with Mixin, Mixin {
-}