Move FinishedSnapshotWrites call back to PostinstallRunnerAction am: 19acf4fe19

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2901827

Change-Id: I94ba3d781d00add55178581e85ec363147676ed5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>