Clean up rust_test_host TEST_MAPPING after default update am: 6be6a10d6d am: 64263e5850 am: 2daac734f6

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro-nested/+/1584272

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I9d99bc730179a0b4093ed04cd3a65e9c6cb9d772