Remove deprecated dart:utf library.

utils/tests/string_encoding/utf8_test.dart

Index: utils/tests/string_encoding/utf8_test.dart
diff --git a/utils/tests/string_encoding/utf8_test.dart b/utils/tests/string_encoding/utf8_test.dart
index 09fee3c055828d03d023056721eb604ed3a1524a..4070426f96f36b9864a885ec6c8568b69b9d9fbb 100755
--- a/utils/tests/string_encoding/utf8_test.dart
+++ b/utils/tests/string_encoding/utf8_test.dart
@@ -5,7 +5,7 @@
 
 library utf8_tests;
 import 'dunit.dart';
-import '../../../lib/utf/utf.dart';
+import '../../../lib/convert/convert.dart';
 
 void main() {
   TestSuite suite = new TestSuite();
@@ -149,6 +149,10 @@ class Utf8Tests extends TestClass {
         "Katakana to utf8");
   }
 
+  List encodeUtf8(String text) => UTF8.encode(text);
+  String decodeUtf8(List bytes) => UTF8.decode(bytes);
+  List utf8ToCodePoints(List bytes) => UTF8.decode(bytes).runes.toList();
+
   void testUtf8bytesToCodepoints() {
     Expect.listEquals([954, 972, 963, 956, 949],
         utf8ToCodepoints([0xce, 0xba, 0xcf, 0x8c, 0xcf,