Add RemoveObserver() in FlocIdProviderImpl::Shutdown()

Bug: 1144907
Change-Id: I5c66ef7b869ada7603fbc7e15c20007c078bb0d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2515044
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Auto-Submit: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Reviewed-by: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823395}

chrome/browser/federated_learning/floc_id_provider_impl.cc

@@ -159,6 +159,8 @@ void FlocIdProviderImpl::Shutdown() {
   if (history_service_)
     history_service_->RemoveObserver(this);
   history_service_ = nullptr;
+
+  g_browser_process->floc_sorting_lsh_clusters_service()->RemoveObserver(this);
 }
 
 void FlocIdProviderImpl::OnURLsDeleted(