Clean up rust_test_host TEST_MAPPING after default update am: b29d50ec96 am: 9f5d956854 am: df7743ea99 am: f21617a5ba

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/num_cpus/+/1591331

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I568bcbf296f0c51d196b2b5bcf0c1be429329e29
diff --git a/TEST_MAPPING b/TEST_MAPPING
deleted file mode 100644
index d64ac43..0000000
--- a/TEST_MAPPING
+++ /dev/null
@@ -1,9 +0,0 @@
-// Generated by cargo2android.py for tests in Android.bp
-{
-  "presubmit": [
-    {
-      "host": true,
-      "name": "tokio-macros_host_test_src_lib"
-    }
-  ]
-}