roll: third_party/pigweed pw_time: Drop board_deps from Zephyr Rust helper

pw_time_backend_zephyr_helper only requires Zephyr headers (@zephyr) to
compile. Depending on @zephyr//:board_deps causes rust_static_library
targets to bundle board support archives into the Rust staticlib,
resulting in duplicate symbol errors during final Zephyr linking.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/490531
Original-Revision: 288d450c5af252c0c3f3b47b27d5e4463995851d

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: d0d713bbd869c5..288d450c5af252
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8669188294867413505
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I52d42bc05232211f0b725a06aeadfe91b05deecd
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/490711
diff --git a/third_party/pigweed b/third_party/pigweed
index d0d713b..288d450 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d0d713bbd869c5499f4b7d88154986260908ced3
+Subproject commit 288d450c5af252c0c3f3b47b27d5e4463995851d