Revert "Convert unittest to use "package:" imports."

pkg/unittest/test/matchers_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.
 
 library unittestTests;
-import 'package:unittest/unittest.dart';
+import '../../../pkg/unittest/lib/unittest.dart';
 part 'test_utils.dart';
 
 doesNotThrow() {}
 doesThrow() { throw 'X'; }
 
 class PrefixMatcher extends BaseMatcher {
   final String _prefix;
   const PrefixMatcher(this._prefix);
   bool matches(item, MatchState matchState) {
     return item is String &&
@@ skipping 510 matching lines @@
       var w = new Widget();
       w.price = 10;
       shouldPass(w, new HasPrice(greaterThan(0)));
       shouldFail(w, new HasPrice(greaterThan(10)),
           'Expected: Widget with a price that is a value greater than <10> '
           'but: price was <10>.');
     });
   });
 }