[roll third_party/pigweed] *: Remove module-level README.md files

These files are unnecessary and mostly out of date.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/188374

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: b2f23b4e8480985..9b5ca82fd24f5be
Roller-URL: https://ci.chromium.org/b/8758523949890760049
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iff061636f8f8156783cf765852bb852964ecf109
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/188376
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index b2f23b4..9b5ca82 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b2f23b4e848098589642a529832bc89117d16bb3
+Subproject commit 9b5ca82fd24f5be96ccfb1a6d61027af263d0c01