Remove fetch option from ExternalSorter

[yyy1000]

Is your feature request related to a problem or challenge?

When I learn Sort implementation for #9170 I found now the fetch option in ExternalSorter is not used since #7721, see below https://github.com/apache/arrow-datafusion/blob/497cb9d46c6f68de6762998c241d0860072c7909/datafusion/physical-plan/src/sorts/sort.rs#L868-L897 I wonder whether it's proper to remove this option to make it cleaner or keep it for possible future use.🤔

Describe the solution you'd like

remove the fetch option and related method

Describe alternatives you've considered

Keep it, maybe useful in future?

Additional context

I can help it if needed.