Remove TEST_MAPPING, failing rust tests am: 19b50d7e67 am: 18f8214edc

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/rust/crates/unicode-xid/+/12295794

Change-Id: If8cfb16574c33ac6463595a5eafc7a0b7b5e9d63