ambient: Clean up one comment

The bug has been fixed. Clean up the comment.

Bug: b/148818448
Test: pass current tests
Change-Id: I460da30ca2d70d8af7e3d1c0efb4ac19415e8217
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212933Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771247}

ash/ambient/backdrop/ambient_backend_controller_impl.cc

@@ -126,9 +126,6 @@ class BackdropURLLoader {
     DCHECK(!simple_loader_);
 
     loader_factory_ = AmbientClient::Get()->GetURLLoaderFactory();
-
-    // TODO(b/148818448): This will reset previous request without callback
-    // called. Handle parallel/sequential requests to server.
     simple_loader_ = network::SimpleURLLoader::Create(
         std::move(resource_request), traffic_annotation);
     simple_loader_->AttachStringForUpload(request_body, kProtoMimeType);