Clean up rust_test_host TEST_MAPPING after default update am: ec0ed42ddd

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/cfg-if/+/1582584

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ie4a45843f3239374cefcd96e975f77f2094ea38b