Clean up rust_test_host TEST_MAPPING after default update am: 7b41568a63 am: ad02e9381d

Original change: https://android-review.googlesource.com/c/platform/external/libchromeos-rs/+/1582586

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ie16fc88e44b7dffa873e10064bc1d48e8c082368