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: Ie0fa4951c497aea13fbcde5e0ffd818b1fcbe0e1
Test: presubmit
Bug: 178646865
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 7bc6ed2..6716814 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -2,10 +2,6 @@
 {
   "presubmit": [
     {
-      "host": true,
-      "name": "libsqlite3-sys_host_test_src_lib"
-    },
-    {
       "name": "libsqlite3-sys_device_test_src_lib"
     }
   ]