Migrate to cargo_embargo. am: e2a9f1d164

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

Change-Id: I3e06b53e61ee815ec28334cd1ad9f69b85dd4812
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>