Clean up rust_test_host TEST_MAPPING after default update am: f706f8b82f am: 1463bab310 am: 0031ebf36b

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro-error/+/1590595

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Icea7721c1583123a31e4e7de0fec0c0e43cfadb6