[roll third_party/pigweed] pw_rpc: Remove unused BUILD dependency

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126500

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a2bc5f4e7b7ca32..858b99a34b69f57
Roller-URL: https://ci.chromium.org/b/8792124894802830769
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I459320c9c53942978ccdf401c0ce384336fbd4dd
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126505
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index a2bc5f4..858b99a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a2bc5f4e7b7ca32096819f5748ce0f20d525e3fe
+Subproject commit 858b99a34b69f577a83ecf8d91fcce2555d1c08f