Clean up rust_test_host TEST_MAPPING after default update

After b/177689340, rust_test_host doesn't need TEST_MAPPING config anymore to run in
presubmit.

Change-Id: Ie84728192b281914b52501d5155b5b8ad7e427a3
Test: presubmit
Bug: 178646865
diff --git a/TEST_MAPPING b/TEST_MAPPING
index eb0c1a4..bc55ed7 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -2,24 +2,12 @@
 {
   "presubmit": [
     {
-      "host": true,
-      "name": "getrandom_host_test_src_lib"
-    },
-    {
       "name": "getrandom_device_test_src_lib"
     },
     {
-      "host": true,
-      "name": "getrandom_host_test_tests_common"
-    },
-    {
       "name": "getrandom_device_test_tests_common"
     },
     {
-      "host": true,
-      "name": "rand_core_host_test_src_lib"
-    },
-    {
       "name": "rand_core_device_test_src_lib"
     }
   ]