Fix developer extension test expectations

runtime/observatory/tests/service/developer_extension_test.dart

Index: runtime/observatory/tests/service/developer_extension_test.dart
diff --git a/runtime/observatory/tests/service/developer_extension_test.dart b/runtime/observatory/tests/service/developer_extension_test.dart
index 5c8e5cd877ef54fde1596b8a8a80ee5488e28529..3ec6a6c6f6511e2de5771c657b06c6514e031b5b 100644
--- a/runtime/observatory/tests/service/developer_extension_test.dart
+++ b/runtime/observatory/tests/service/developer_extension_test.dart
@@ -145,7 +145,6 @@ var tests = [
     } on ServerRpcException catch (e, st) {
       expect(e.code, equals(ServiceExtensionResponse.extensionError));
       expect(e.message, stringContainsInOrder([
-          'Error in extension `ext..languageError`:',
           'developer_extension_test.dart',
           'semicolon expected']));
     }