Clean up rust_test_host TEST_MAPPING after default update am: 5e39018bbf am: af4529ec5a am: 878a689fbc

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

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I232bc2de8e6d8f790ab8c1c3d5c274ca94b41fca
diff --git a/TEST_MAPPING b/TEST_MAPPING
deleted file mode 100644
index fe12edb..0000000
--- a/TEST_MAPPING
+++ /dev/null
@@ -1,9 +0,0 @@
-// Generated by cargo2android.py for tests in Android.bp
-{
-  "presubmit": [
-    {
-      "host": true,
-      "name": "protobuf-codegen_host_test_src_lib"
-    }
-  ]
-}