Revert "Map all partitions before calling FinishUpdate for VAB as well" am: 1cbbbb0772 am: fa0a7e87ab

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3480104

Change-Id: Ie2b1cf1cface77c81252c0ee3652d933be759320
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>