Delete APK snapshots during restoration (3/n)

The snapshots are no longer needed after restore is done.

We do this in keeping with the fact that apk/apex code data is
deleted immediately after the rollback is committed.

See go/rollbackmanager-snapshot-deletion for more details.

Bug: 151805360
Test: N/A. Will be added in the next CL.

Merged-In: I5a7540aa08922c4b0c617c9cb37e1bec2ff23fc1
Change-Id: I5a7540aa08922c4b0c617c9cb37e1bec2ff23fc1