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: I9a157c48315c4b01e735c309ff0b015a91b386f7
Test: presubmit
Bug: 178646865
diff --git a/TEST_MAPPING b/TEST_MAPPING
index c3fc666..4c07fed 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -2,17 +2,9 @@
 {
   "presubmit": [
     {
-      "host": true,
-      "name": "bitflags_host_test_src_lib"
-    },
-    {
       "name": "bitflags_device_test_src_lib"
     },
     {
-      "host": true,
-      "name": "libsqlite3-sys_host_test_src_lib"
-    },
-    {
       "name": "libsqlite3-sys_device_test_src_lib"
     }
   ]