update_engine: Delete android things policy

Android things policy not used.

BUG=b:171829801
TEST=none

Change-Id: Ibf14e72ac9061dcad7c4b291474834529681c395
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2518384
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/update_manager/policy.h b/update_manager/policy.h
index 7543ea9..595fb7c 100644
--- a/update_manager/policy.h
+++ b/update_manager/policy.h
@@ -303,9 +303,7 @@
   DISALLOW_COPY_AND_ASSIGN(Policy);
 };
 
-// Get system dependent (Chrome OS vs. Android) policy
-// implementation. Implementations can be found in chromeos_policy.cc and
-// android_things_policy.cc.
+// Get system dependent policy implementation.
 std::unique_ptr<Policy> GetSystemPolicy();
 
 }  // namespace chromeos_update_manager