remove unused field in test (dart-lang/markdown#179)

pkgs/markdown/test/util.dart

diff --git a/pkgs/markdown/test/util.dart b/pkgs/markdown/test/util.dart
index 6b8e312..b54433f 100644
--- a/pkgs/markdown/test/util.dart
+++ b/pkgs/markdown/test/util.dart
@@ -12,8 +12,6 @@
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
-final _indentPattern = new RegExp(r"^\(indent (\d+)\)\s*");
-
 /// Run tests defined in "*.unit" files inside directory [name].
 void testDirectory(String name) {
   for (var dataCase