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

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

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ic64b05bb09dae3e398ef2b1759a4616a8c7a0f01