Remove deprecated fields from update_metadata protobuf am: 9ae7dc6045 am: 2d426ae71c

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2056748

Change-Id: I7edf93275ccff4dd8fb4b9bd88e331a83caa1a59
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>