Clean up rust_test_host TEST_MAPPING after default update am: 5e39018bbf am: af4529ec5a

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/protobuf-codegen/+/1582279

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I041047e92b7fd3f197c8d46f31bc688ab19df666