Fix developer extension test expectations

runtime/observatory/tests/service/developer_extension_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:observatory/cpu_profile.dart';
@@ skipping 127 matching lines @@
     expect(result['method'], equals('ext..success'));
     expect(result['parameters']['isolateId'], isNotNull);
     expect(result['parameters']['apple'], equals('banana'));
 
 
     try {
       result = await isolate.invokeRpcNoUpgrade('ext..languageError', {});
     } 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']));
     }
   },
 ];
 
 main(args) async => runIsolateTests(args, tests, testeeConcurrent:test);