Clean up rust_test_host TEST_MAPPING after default update am: 812115654b

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/unicode-segmentation/+/1582857

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Iacdcdc2b6591403462a0bf0d23534a13b60612ca
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 8744265..60b40b7 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -2,14 +2,6 @@
 {
   "presubmit": [
     {
-      "host": true,
-      "name": "structopt-derive_host_test_src_lib"
-    },
-    {
-      "host": true,
-      "name": "heck_host_test_src_lib"
-    },
-    {
       "name": "heck_device_test_src_lib"
     }
   ]