Migrate to cargo_embargo. am: 8db550a9e9

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

Change-Id: I7089c1a741b2b4895f6b543b4e80ad53cf02fef8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>