Upgrade rust/crates/futures-channel to 0.3.12

Test: make
Change-Id: I2cd8faf5d73c915d9dfc92c1bf7232e31010c05c
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 7d1919a..7e10dd0 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -1,11 +1,7 @@
-// Generated by cargo2android.py for tests in Android.bp
+// Generated by update_crate_tests.py for tests that depend on this crate.
 {
   "presubmit": [
     {
-      "host": true,
-      "name": "futures-util_host_test_src_lib"
-    },
-    {
       "name": "futures-util_device_test_src_lib"
     }
   ]