Clean up rust_test_host TEST_MAPPING after default update am: b92a85ff64

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/bencher/+/1582326

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I837d61a4a4430dcfeef9e934e5cceeb81cafacd7