cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/core/bool.dart

 part of dart.core;
 
 class bool {
-  @patch factory bool.fromEnvironment(String name, {bool defaultValue: false}) {
+  factory bool.fromEnvironment(String name, {bool defaultValue: false}) {
     throw new UnsupportedError(
         'bool.fromEnvironment can only be used as a const constructor');
   }
   String toString() {
     return this ? "true" : "false";
   }
 }