Remove dart backend

test/dart_codegen/expect/convert/codec.dart

-part of dart.convert;
- abstract class Codec<S, T> {const Codec();
- T encode(S input) => encoder.convert(input);
- S decode(T encoded) => decoder.convert(encoded);
- Converter<S, T> get encoder;
- Converter<T, S> get decoder;
- Codec<S, dynamic> fuse(Codec<T, dynamic> other) {
-  return new _FusedCodec<S, T, dynamic>(this, other);
-  }
- Codec<T, S> get inverted => new _InvertedCodec<T, S>(this);
-}
- class _FusedCodec<S, M, T> extends Codec<S, T> {final Codec<S, M> _first;
- final Codec<M, T> _second;
- Converter<S, T> get encoder => ((__x0) => DEVC$RT.cast(__x0, DEVC$RT.type((Converter<S, dynamic> _) {
-}
-), DEVC$RT.type((Converter<S, T> _) {
-}
-), "CompositeCast", """line 87, column 34 of dart:convert/codec.dart: """, __x0 is Converter<S, T>, false))(_first.encoder.fuse(_second.encoder));
- Converter<T, S> get decoder => ((__x1) => DEVC$RT.cast(__x1, DEVC$RT.type((Converter<T, dynamic> _) {
-}
-), DEVC$RT.type((Converter<T, S> _) {
-}
-), "CompositeCast", """line 88, column 34 of dart:convert/codec.dart: """, __x1 is Converter<T, S>, false))(_second.decoder.fuse(_first.decoder));
- _FusedCodec(this._first, this._second);
-}
- class _InvertedCodec<T, S> extends Codec<T, S> {final Codec<S, T> _codec;
- _InvertedCodec(Codec<S, T> codec) : _codec = codec;
- Converter<T, S> get encoder => _codec.decoder;
- Converter<S, T> get decoder => _codec.encoder;
- Codec<S, T> get inverted => _codec;
-}