cleanup patch generation to preseve comments and remove @patch

test/generated_sdk/lib/core/regexp.dart

Index: test/generated_sdk/lib/core/regexp.dart
diff --git a/test/generated_sdk/lib/core/regexp.dart b/test/generated_sdk/lib/core/regexp.dart
index 5c87a97a95f72b7b628d0c4c53f5cf3405880699..d5ef3db7f6d0137cf80a65a6c5aee396cd223da4 100644
--- a/test/generated_sdk/lib/core/regexp.dart
+++ b/test/generated_sdk/lib/core/regexp.dart
@@ -118,7 +118,12 @@ abstract class Match {
  *     Iterable<Match> matches = exp.allMatches(str);
  */
 abstract class RegExp implements Pattern {
-  @patch
+  /**
+   * Constructs a regular expression.
+   *
+   * Throws a [FormatException] if [source] is not valid regular
+   * expression syntax.
+   */
   factory RegExp(String source,
                        {bool multiLine: false,
                         bool caseSensitive: true})