cleanup patch generation to preseve comments and remove @patch

test/dart_codegen/expect/collection/hash_set.dart

 part of dart.collection;
 
 abstract class _HashSetBase<E> extends SetBase<E> {
   Set<E> difference(Set<Object> other) {
     Set<E> result = _newSet();
     for (var element in this) {
       if (!other.contains(element)) result.add(DDC$RT.cast(element, dynamic, E,
           "CastGeneral",
           """line 17, column 48 of dart:collection/hash_set.dart: """,
           element is E, false));
     }
     return result;
   }
   Set<E> intersection(Set<Object> other) {
     Set<E> result = _newSet();
     for (var element in this) {
       if (other.contains(element)) result.add(DDC$RT.cast(element, dynamic, E,
           "CastGeneral",
           """line 25, column 47 of dart:collection/hash_set.dart: """,
           element is E, false));
     }
     return result;
   }
   Set<E> _newSet();
   Set<E> toSet() => _newSet()..addAll(this);
 }
 abstract class HashSet<E> implements Set<E> {
-  @patch factory HashSet({bool equals(E e1, E e2), int hashCode(E e),
+  factory HashSet({bool equals(E e1, E e2), int hashCode(E e),
       bool isValidKey(potentialKey)}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
           return new _HashSet<E>();
         }
         hashCode = _defaultHashCode;
       } else {
         if (identical(identityHashCode, hashCode) &&
             identical(identical, equals)) {
           return new _IdentityHashSet<E>();
         }
         if (equals == null) {
           equals = _defaultEquals;
         }
       }
     } else {
       if (hashCode == null) {
         hashCode = _defaultHashCode;
       }
       if (equals == null) {
         equals = _defaultEquals;
       }
     }
     return new _CustomHashSet<E>(equals, hashCode, isValidKey);
   }
-  @patch factory HashSet.identity() = _IdentityHashSet<E>;
+  factory HashSet.identity() = _IdentityHashSet<E>;
   factory HashSet.from(Iterable elements) {
     HashSet<E> result = new HashSet<E>();
     for (E e in elements) result.add(e);
     return result;
   }
   Iterator<E> get iterator;
 }