update OTA script in tm-mainline-prod to the latest version.

The last change in tm-mainline-prod was last year (aosp/2040556), did a copy of current version in udc-dev.

Test: local ota
Bug: 279622634
Change-Id: I6563122f21d7213bfa7200e28cdfa69bd95aa3e2
Merged-In: Iaa317a3a4b8addbca8ea987aee9953c78fa1a679
diff --git a/scripts/update_payload/test_utils.py b/scripts/update_payload/test_utils.py
index e153669..7005827 100644
--- a/scripts/update_payload/test_utils.py
+++ b/scripts/update_payload/test_utils.py
@@ -27,7 +27,7 @@
 
 from update_payload import common
 from update_payload import payload
-from update_payload import update_metadata_pb2
+import update_metadata_pb2
 
 
 class TestError(Exception):