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

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

Change-Id: I7fb217728b72d1c1b0ced2f624ea69645c71970f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>