Several interface cleanups.

 - Kill Close in Persistent and document interface.
 - Extract batching behavior into interface.
 - Kill IteratorManager, which was used for unknown reasons.
Several important cleanups and deprecations.

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.