Delete a bunch of packages that are now on GitHub.

pkg/string_scanner/test/utils.dart

-// Copyright (c) 2014, 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 string_scanner.test.utils;
-
-import 'package:string_scanner/string_scanner.dart';
-import 'package:unittest/unittest.dart';
-
-/// Returns a matcher that asserts that a closure throws a [FormatException]
-/// with the given [message].
-Matcher throwsStringScannerException(String text) {
-  return throwsA(predicate((error) {
-    expect(error, new isInstanceOf<StringScannerException>());
-    expect(error.span.text, equals(text));
-    return true;
-  }));
-}