Migrate to cargo_embargo. am: d19ea6527f am: 538652dfb4

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-channel/+/2833071

Change-Id: I18ca7af1b7c8f32bd14835d7f010bb6d580cc159
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>