Clean up cc_test TEST_MAPPING after default update

After b/179092189, cc_test host_supported:true doesn't need TEST_MAPPING config anymore to
run in presubmit.

Change-Id: I4985b9f1bc0d8bef24df447720d138b1a5072c9c
Test: presubmit
Bug: 178646865
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 52cff94..da7fca1 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -52,10 +52,6 @@
       "name": "memunreachable_unit_test"
     },
     {
-      "name": "memunreachable_unit_test",
-      "host": true
-    },
-    {
       "name": "memunreachable_binder_test"
     },
     {