Remove deprecated Strings class.

pkg/yaml/test/yaml_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 yaml_test;
 
 import 'package:unittest/unittest.dart';
 import 'package:yaml/yaml.dart';
 import 'package:yaml/deep_equals.dart';
 // TODO(jmesserly): we should not be reaching outside the YAML package
@@ skipping 1332 matching lines @@
 
     test('[Example 7.22]', () {
       Expect.throws(() => loadYaml(cleanUpLiteral(
         """
         [ foo
          bar: invalid ]""")));
 
       // TODO(nweiz): enable this when we throw an error for long keys
       // var dotList = [];
       // dotList.insertRange(0, 1024, ' ');
-      // var dots = Strings.join(dotList, '');
+      // var dots = dotList.join();
       // Expect.throws(() => loadYaml('[ "foo...$dots...bar": invalid ]'));
     });
   });
 
   group('7.5: Flow Nodes', () {
     test('[Example 7.23]', () {
       expectYamlLoads([["a", "b"], {"a": "b"}, "a", "b", "c"],
         """
         - [ a, b ]
         - { a: b }
@@ skipping 506 matching lines @@
         A null: null
         Also a null: # Empty
         Not a null: ""
         Booleans: [ true, True, false, FALSE ]
         Integers: [ 0, 0o7, 0x3A, -19 ]
         Floats: [ 0., -0.0, .5, +12e03, -2E+05 ]
         Also floats: [ .inf, -.Inf, +.INF, .NAN ]''');
     });
   });
 }