Don't delete expired snapshots or environments records unless their associated data objects have been deleted

[izeigerman]

We currently delete environment/snapshot records first, and only then do we attempt to clean up the views/tables associated with them.

This means that if a view or table deletion fails for any reason, the deletion process won't be reattempted later, as any information about its existence has already been removed from the state.

We need to change the order of operations and delete a record from the state only after the associated data object has been successfully deleted.