[roll third_party/pigweed] pw_rpc: Delete dead code for raw sync RPCs

The raw synchronous API was removed a while ago, but some dead code
remained behind.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/112011

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 72940d68c20122e..bee840f3cf39fe2
Roller-URL: https://ci.chromium.org/b/8801921018054179681
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I7dba23dbb7c72bd73452d37cfc46a7c066836666
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/112138
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 72940d6..bee840f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 72940d68c20122e1829d1be9c421b9d36ec02bc0
+Subproject commit bee840f3cf39fe296e95202f27b701beec48f58f