Removed fixed dependencies

packages/convert/lib/src/hex.dart

+// Copyright (c) 2015, 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 convert.hex;
+
+import 'dart:convert';
+
+import 'hex/encoder.dart';
+import 'hex/decoder.dart';
+
+export 'hex/encoder.dart' hide hexEncoder;
+export 'hex/decoder.dart' hide hexDecoder;
+
+/// The canonical instance of [HexCodec].
+const hex = const HexCodec._();
+
+/// A codec that converts byte arrays to and from hexadecimal strings, following
+/// [the Base16 spec][rfc].
+///
+/// [rfc]: https://tools.ietf.org/html/rfc4648#section-8
+///
+/// This should be used via the [hex] field.
+class HexCodec extends Codec<List<int>, String> {
+  HexEncoder get encoder => hexEncoder;
+  HexDecoder get decoder => hexDecoder;
+
+  const HexCodec._();
+}