Allow building for device.

Ran 'cargo2android.py --run --device' and reverted the removal of the
comments.

Bug: 158290206
Test: mm
Change-Id: Ie60d46525da122f308896b6107a58ebb9415a390

Android.bp

diff --git a/Android.bp b/Android.bp
index a2dff23..eb6a4c4 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,7 +1,8 @@
-// This file is generated by cargo2android.py.
+// This file is generated by cargo2android.py --run --device.
 
-rust_library_host_rlib {
+rust_library_rlib {
     name: "libfutures_executor",
+    host_supported: true,
     crate_name: "futures_executor",
     srcs: ["src/lib.rs"],
     edition: "2018",