[roll third_party/pigweed] pw_rpc: Revert change to hold lock while calling on_completed wrapper

This partially reverts commit adc77a345db134d07c5ff3e5af4affae4e7ea21b.
Holding the lock while invoking the on_completed wrapper may be causing
deadlocks in some configurations.

Original-Bug: b/234876851
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126454

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: adc77a345db134d..aabb87ddf82decb
Roller-URL: https://ci.chromium.org/b/8792145816939675345
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Idb2d2c5474554c20cc52e9ccf0995b62114c7403
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126483
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index adc77a3..aabb87d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit adc77a345db134d07c5ff3e5af4affae4e7ea21b
+Subproject commit aabb87ddf82decb273d8a432781c1bdbf2a2d8fc