[roll third_party/pigweed] python: Remove references to non-existing setup.py

In commit e1b56dbcd84a836da16f1b34d21edaa157782983, there
was the removal of setup.py scripts, but references to them
remain in the code. This patch is removing them.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/182770

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: aaf149d9e874535..c8c31a063f54a11
Roller-URL: https://ci.chromium.org/b/8761991136700720705
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie38ac0ee66e07bf66febe159ed13ae3db193b078
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/184631
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index aaf149d..c8c31a0 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit aaf149d9e87453549c3893de3a09d6e2e65009ec
+Subproject commit c8c31a063f54a11ffdc32635c2d516876f4cc94b