[roll third_party/pigweed] pw_rpc: Make channel output to Server::ProcessPacket optional

This updates the RPC server to not require a channel output as an
argument to the ProcessPacket function. This output is only used to
create dynamic channels. Dynamic channels are not properly supported
yet, and some projects will never use them. Requiring a channel output
argument needlessly complicates RPC setup for these projects.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/71760

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a19e285f417b081..ba93a434b8301df
Roller-URL: https://ci.chromium.org/b/8827735469024565873
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827735469024565873
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib0adbd34ba1c50bbfd5854e1adca15c2dd5c8081
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/74880
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 a19e285..ba93a43 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a19e285f417b08146234a54878e826ef61b9defa
+Subproject commit ba93a434b8301df216d869764ea360660c521b31