[roll third_party/pigweed] bazel: Localize remaining backend label flags

This CL moves those backend label flags which had to be moved gradually
because downstream projects used them. All downstream users have now
been updated, so these flags can be removed.

Original-Fixed: 329441699
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/199036

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 8ac329d75f93ded..ff2cbf8c82c8a69
Roller-URL: https://ci.chromium.org/b/8752461711982629185
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I00959702e21e19db8c6b806d753e3e4fa52d61db
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/199571
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 8ac329d..ff2cbf8 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 8ac329d75f93dedc7a7278cdbdbb07b0107b7282
+Subproject commit ff2cbf8c82c8a6901a63f2fc4e0cea273a2d6713