Clean up rust_test_host TEST_MAPPING after default update am: 58765e4095

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/getrandom/+/1584503

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ia73e02532cf3d0d6510d3b57348c15370dcd40d7