update_engine: remove is_rollback am: ad1eaead8f am: 85148e2d8c

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3203012

Change-Id: Ibf87fea82394d6e97e520d66391a2597764517ec
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>