[roll third_party/pigweed] pw_unit_test: Remove obsolete label flag

It has been a no-op for some time, and since cl/603736296 there are no
remaining references to it in internal downstream projects.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/190557

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: b31d94d6d972466..0d764ab24825195
Roller-URL: https://ci.chromium.org/b/8756731336002003617
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I73218332917d4b473e0471e2579055ae6adbab9e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/190710
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 b31d94d..0d764ab 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit b31d94d6d97246655c010cf9043692f511a8d7cd
+Subproject commit 0d764ab2482519535d34b36d2fdb7b61aa26a092