pkg/third_party/html5lib: lots of cleanup

pkg/third_party/html5lib/test/tokenizer_test.dart

Index: pkg/third_party/html5lib/test/tokenizer_test.dart
diff --git a/pkg/third_party/html5lib/test/tokenizer_test.dart b/pkg/third_party/html5lib/test/tokenizer_test.dart
index b9e43fedbca338baedf4fd19983b4a79fee64ece..439e44000c3322f5050a5d7e658df28c81e7deed 100644
--- a/pkg/third_party/html5lib/test/tokenizer_test.dart
+++ b/pkg/third_party/html5lib/test/tokenizer_test.dart
@@ -1,17 +1,14 @@
 library tokenizer_test;
 
 // Note: mirrors used to match the getattr usage in the original test
-import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:mirrors';
 import 'package:path/path.dart' as pathos;
 import 'package:unittest/unittest.dart';
 import 'package:html5lib/src/char_encodings.dart';
-import 'package:html5lib/src/constants.dart' as constants;
 import 'package:html5lib/src/token.dart';
 import 'package:html5lib/src/tokenizer.dart';
-import 'package:html5lib/src/utils.dart';
 import 'package:utf/utf.dart';
 import 'support.dart';