roll: third_party/pigweed pw_system: Use a lambda instead of ThreadCore

ThreadCore is not recommended for new code since pw::Thread now uses
pw::Function. Also, remove unused function declaration

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/244512
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: 886cebe93469153cac472957058dbc5676d1d7c6

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: c3338f9b4f108b..886cebe9346915
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8733139324887916353
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8fd742507a27072f365dda2eff9114792691e62f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/244408
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index c3338f9..886cebe 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c3338f9b4f108b089efe1be9ae28f61354fa6bd2
+Subproject commit 886cebe93469153cac472957058dbc5676d1d7c6