Disable AvatarMenu in ExtensionAppShimHandler

The AvatarMenu is out-living ProfileAttributesStorage, and causing a
use after free. Disable its allocation for the moment.

There are a menu of follow-up fixes available:
- Ensure ExtensionAppShimHandler be terminated before
  ProfileAttributesStorage (and consider using a CheckedObserver
  instead of an UncheckedObserver).
- Make AvatarMenu use a weak pointer to ProfileAttributesStorage and
  allow ExtensionAppShimHandler to outlive ProfileAttributesStorage.

TBR=dominickn

Bug: 1008947
Change-Id: I0419c7427c4fd37c4a5fa583155ddf06ccf93d57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1830917Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700989}

chrome/browser/apps/app_shim/extension_app_shim_handler_mac.cc

@@ -262,9 +262,8 @@ bool ExtensionAppShimHandler::AppState::IsMultiProfile() const {
 
 std::unique_ptr<AvatarMenu> ExtensionAppShimHandler::Delegate::CreateAvatarMenu(
     AvatarMenuObserver* observer) {
-  ProfileManager* profile_manager = g_browser_process->profile_manager();
-  return std::make_unique<AvatarMenu>(
-      &profile_manager->GetProfileAttributesStorage(), observer, nullptr);
+  // TODO(https://crbug.com/1008947): Fix use-after-free caused by AvatarMenu.
+  return nullptr;
 }
 
 Profile* ExtensionAppShimHandler::Delegate::ProfileForPath(