Remove AST-hack for multi-field declarations.

tests/compiler/dart2js/serialization/test_data.dart

Index: tests/compiler/dart2js/serialization/test_data.dart
diff --git a/tests/compiler/dart2js/serialization/test_data.dart b/tests/compiler/dart2js/serialization/test_data.dart
index 9fbd2236cc3353b67f5ad1b7986b63d32c5432ce..73d088fd0d5cb069d81b357be0816b1ea1e8afcd 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -673,6 +673,18 @@ class ConstClass {
 }
 ''',
   }),
+
+  const Test('Multi variable declaration', const {
+    'main.dart': '''
+import 'a.dart';
+
+main() => y;
+''',
+  }, preserializedSourceFiles: const {
+    'a.dart': '''
+var x, y = 2;
+''',
+  }),
 ];
 
 class Test {