cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/core/expando.dart

 part of dart.core;
 
 class Expando<T> {
   final String name;
-  @patch Expando([String name]) : this.name = name;
+  Expando([String name]) : this.name = name;
   String toString() => "Expando:$name";
-  @patch T operator [](Object object) {
+  T operator [](Object object) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
     return ((__x21) => DDC$RT.cast(__x21, dynamic, T, "CastGeneral",
-            """line 44, column 12 of dart:core/expando.dart: """, __x21 is T,
+            """line 55, column 12 of dart:core/expando.dart: """, __x21 is T,
             false))(
         (values == null) ? null : Primitives.getProperty(values, _getKey()));
   }
-  @patch void operator []=(Object object, T value) {
+  void operator []=(Object object, T value) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
     if (values == null) {
       values = new Object();
       Primitives.setProperty(object, _EXPANDO_PROPERTY_NAME, values);
     }
     Primitives.setProperty(values, _getKey(), value);
   }
 }