Clean up rust_test_host TEST_MAPPING after default update am: d4bc4a1f1e am: b79273b585 am: 4c677a04f2

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-util/+/1582281

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I46fd95d4eaf661708a3df7c38df6225d1fab4934