update_engine: remove global cow version am: c5be0d2159 am: 5f9de8833a

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3019783

Change-Id: Ia9df3b8074174466230cd36c806f863d41802f64
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>