Clean up rust_test_host TEST_MAPPING after default update am: 466121f669 am: baa94cf971 am: c65764e24f am: 0531ec76c3

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt-derive/+/1584431

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ie730bb0fb8c617974f9de9cbd5c018cb63cf0c06
diff --git a/TEST_MAPPING b/TEST_MAPPING
deleted file mode 100644
index 1e756de..0000000
--- a/TEST_MAPPING
+++ /dev/null
@@ -1,9 +0,0 @@
-// Generated by cargo2android.py for tests in Android.bp
-{
-  "presubmit": [
-    {
-      "host": true,
-      "name": "structopt-derive_host_test_src_lib"
-    }
-  ]
-}