Remove Expect from core library.

tests/compiler/dart2js/closure_codegen_test.dart

 // Copyright (c) 2012, 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.
 // Test that parameters keep their names in the output.
 
+import "package:expect/expect.dart";
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 
 const String TEST_INVOCATION0 = r"""
 main() {
   var o = null;
   o();
 }
 """;
 
@@ skipping 38 matching lines @@
   String generated = compileAll(TEST_BAILOUT);
   RegExp regexp = new RegExp(r'call\$0: function');
   Iterator<Match> matches = regexp.allMatches(generated).iterator;
   checkNumberOfMatches(matches, 1);
 }
 
 main() {
   closureInvocation();
   closureBailout();
 }