Migrate to cargo_embargo. am: 8db550a9e9

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/threadpool/+/2828054

Change-Id: I45e5492bfb159f56534d3a731e82bf76fc6b0b72
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>