Remove unused field save_rollback_data am: 399bd4dae1 am: 99f428ff1e

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3391041

Change-Id: I0dfaeff40684d44e552126296f37bd0e9e392d17
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>