Clean up rust_test_host TEST_MAPPING after default update am: ab7dbba14c

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro-error-attr/+/1584352

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I3d088f9d932017b657ee1a984bb501f52a0274f9