[roll] Roll third_party/pigweed Revert "pw_bluetooth_proxy: Use std::lock_guard"

This reverts commit 54ca0db892863f6d278dc9ca5be92591d1b9f98b.

Reason for revert: Breaks downstream client

Original-Bug: 377889745

Original change's description:
> pw_bluetooth_proxy: Use std::lock_guard
>
> Now that std::lock_guard is available to downstream clients, stop
> manually locking/unlocking mutexes.
>
> Change-Id: I7104ccfd473791e9df0e935db03e8ea6aff67e9d
> Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/241192
> Reviewed-by: David Rees <[email protected]>
> Docs-Not-Needed: Austin Foxley <[email protected]>
> Commit-Queue: Auto-Submit <[email protected]>
> Pigweed-Auto-Submit: Austin Foxley <[email protected]>
> Lint: Lint 🤖 <[email protected]>

# Not skipping CQ checks because original CL landed > 1 day ago.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/247633
Original-Revision: b2288d8bc5b9098343d3d9b76c6b3f0d38ddb948
GitOrigin-RevId: 035db15fd92b65f12bfeeebf4ca906dc5c8e5958
Change-Id: I5b7cdf5230ccc0071314fe83b915aa821541f9f2

Author: Matthew Sedam

third_party/flower

@@ -504,7 +504,7 @@
              path="third_party/pigweed/src"
              remote="https://fuchsia.googlesource.com/third_party/pigweed.googlesource.com/pigweed/pigweed"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="d19799902cd04939b38ca9c8f08e068710b19d95"/>
+             revision="b2288d8bc5b9098343d3d9b76c6b3f0d38ddb948"/>
     <project name="third_party/github.com/google/python_portpicker"
              gitsubmoduleof="fuchsia"
              path="third_party/python_portpicker/src"