[Extensions] Update notification system observer test to use manifest v2

Update notification_system_observer_unittest.cc to generate
extensions with manifest_version 2.

Bug: 816679
Change-Id: Ida57ff94738d3ec7fcfb207b8495d7a31d784a94
Reviewed-on: https://chromium-review.googlesource.com/1008607Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549990}

chrome/browser/notifications/notification_system_observer_unittest.cc

@@ -19,13 +19,7 @@
 namespace {
 scoped_refptr<const extensions::Extension> CreateGoodExtension(
     const std::string& name) {
-  return extensions::ExtensionBuilder()
-      .SetManifest(extensions::DictionaryBuilder()
-                       .Set("name", name)
-                       .Set("version", "1.0")
-                       .Build())
-      .SetID(crx_file::id_util::GenerateId(name))
-      .Build();
+  return extensions::ExtensionBuilder(name).Build();
 }
 }  // namespace