update_engine: remove global cow version am: c5be0d2159

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

Change-Id: I5e7c80892a47aeff1dd3ff2af68600b6a47224de
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>