Revert "Regenerate checked-in update_metadata_pb2.py with aprotoc" am: 2e3cdae869

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1567041

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I76cfa8537d3740cc7dfa86ee132de16ddabefcd2