[service worker] Remove unnecessary comment about the correct rfh

This CL removes comment for a closed bug.
As the bug comments concluded, rfh look up is always safe with render
process id and frame id. Thus, we do not need this comment.

Bug: 1012238
Change-Id: I3b21ca1faca405a40f3ec7ca5c1b64d410d91592
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1909054
Commit-Queue: Yuzu Saijo <yuzus@chromium.org>
Auto-Submit: Yuzu Saijo <yuzus@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714146}

content/browser/service_worker/service_worker_provider_host.cc

@@ -786,7 +786,6 @@ void ServiceWorkerProviderHost::OnBeginNavigationCommit(int render_process_id,
       ServiceWorkerContext::IsServiceWorkerOnUIEnabled() &&
       provider_type() == blink::mojom::ServiceWorkerProviderType::kForWindow) {
     auto* rfh = RenderFrameHostImpl::FromID(render_process_id_, frame_id_);
-    // At this point, |rfh| should point at the correct one. (crbug.com/1012238)
     // |rfh| may be null in tests (but it should not happen in production).
     if (rfh)
       rfh->AddServiceWorkerProviderHost(this);