cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/convert/utf.dart

 part of dart.convert;
 
 const int UNICODE_REPLACEMENT_CHARACTER_RUNE = 0xFFFD;
 const int UNICODE_BOM_CHARACTER_RUNE = 0xFEFF;
 const Utf8Codec UTF8 = const Utf8Codec();
 class Utf8Codec extends Encoding {
   final bool _allowMalformed;
   const Utf8Codec({bool allowMalformed: false})
       : _allowMalformed = allowMalformed;
   String get name => "utf-8";
@@ skipping 165 matching lines @@
     } else {
       stringSink = new StringConversionSink.from(sink);
     }
     return stringSink.asUtf8Sink(_allowMalformed);
   }
   Stream<String> bind(Stream<List<int>> stream) => ((__x31) => DDC$RT.cast(
       __x31, DDC$RT.type((DDC$async$.Stream<dynamic> _) {}),
       DDC$RT.type((DDC$async$.Stream<String> _) {}), "CastDynamic",
       """line 361, column 52 of dart:convert/utf.dart: """,
       __x31 is DDC$async$.Stream<String>, false))(super.bind(stream));
-  @patch Converter<List<int>, dynamic> fuse(Converter<String, dynamic> next) {
+  Converter<List<int>, dynamic> fuse(Converter<String, dynamic> next) {
     return super.fuse(next);
   }
 }
 const int _ONE_BYTE_LIMIT = 0x7f;
 const int _TWO_BYTE_LIMIT = 0x7ff;
 const int _THREE_BYTE_LIMIT = 0xffff;
 const int _FOUR_BYTE_LIMIT = 0x10ffff;
 const int _SURROGATE_MASK = 0xF800;
 const int _SURROGATE_TAG_MASK = 0xFC00;
 const int _SURROGATE_VALUE_MASK = 0x3FF;
@@ skipping 145 matching lines @@
       }
       break loop;
     }
     if (expectedUnits > 0) {
       _value = value;
       _expectedUnits = expectedUnits;
       _extraUnits = extraUnits;
     }
   }
 }