Migrate to cargo_embargo. am: e2a9f1d164 am: 76964361b1

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rand_chacha/+/2822009

Change-Id: I786097578b06f51b10a5d40cfce5a6318609e3d6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>