EachFunc is deprecated.
Remove deprecated ``Pair`` and ``GetAll``.
These were originally used for forensic and the old gorest impl.
Nothing today in the user-facing path nor the tests uses them,
especially since the advent of the ForEach protocol in the
interface.
- Kill Close in Persistent and document interface.
- Extract batching behavior into interface.
- Kill IteratorManager, which was used for unknown reasons.