[C++][Acero] Use implicit_ordering for asof_join rather than require_sequenced_output

[EnricoMi]

Describe the enhancement requested

Changes in #44083 (GH-41706) unnecessarily sequences batches retrieved from scanner where it only requires the batches to provide index according to implicit input order.

Setting implicit_ordering causes existing code to set batch index, which is then available to the asof_join node to sequence the batches int input order. This replaces some of #44083 changes.

Some code introduced by #44083 turns out to not be required and should be reverted.

Component(s)

C++