[roll third_party/pigweed] pw_log: Move pw_log proto

Declare log.proto in pw_log rather than pw_log_proto. The log proto is
properly part of pw_log, rather than a standalone module.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/47220

third_party/pigweed Rolled-Commits: c24e33273f1e5ae..76c3a5cd4660a15
Roller-URL: https://ci.chromium.org/b/8846118433630903552
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8846118433630903552
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib54a08626184dad550278169175d15595c55bf95
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/47087
Reviewed-by: 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 c24e332..76c3a5c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c24e33273f1e5ae2f68b880d08e1928a9737d7b6
+Subproject commit 76c3a5cd4660a15509c55b1038e0e1d40c0171ae