cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/collection/linked_hash_set.dart

 part of dart.collection;
 
 abstract class LinkedHashSet<E> implements HashSet<E> {
-  @patch factory LinkedHashSet({bool equals(E e1, E e2), int hashCode(E e),
+  factory LinkedHashSet({bool equals(E e1, E e2), int hashCode(E e),
       bool isValidKey(potentialKey)}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
           return new _LinkedHashSet<E>();
         }
         hashCode = _defaultHashCode;
       } else {
         if (identical(identityHashCode, hashCode) &&
             identical(identical, equals)) {
           return new _LinkedIdentityHashSet<E>();
         }
         if (equals == null) {
           equals = _defaultEquals;
         }
       }
     } else {
       if (hashCode == null) {
         hashCode = _defaultHashCode;
       }
       if (equals == null) {
         equals = _defaultEquals;
       }
     }
     return new _LinkedCustomHashSet<E>(equals, hashCode, isValidKey);
   }
-  @patch factory LinkedHashSet.identity() = _LinkedIdentityHashSet<E>;
+  factory LinkedHashSet.identity() = _LinkedIdentityHashSet<E>;
   factory LinkedHashSet.from(Iterable<E> elements) {
     LinkedHashSet<E> result = new LinkedHashSet<E>();
     for (final E element in elements) {
       result.add(element);
     }
     return result;
   }
   void forEach(void action(E element));
   Iterator<E> get iterator;
 }