Migrate to cargo_embargo. am: 251a0c3b9f

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/utf-8/+/2852606

Change-Id: I8fb2ddda1a3874a8d0ba66822be089a8f5885714
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>