Remove RowAccumulators and datafusion-row #6968
                
     Merged
            
            
          
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Which issue does this PR close?
Part of #6798
Part of #6889
Rationale for this change
The new grouping introduced in #6904 is faster than
RowAccumulatorsand thus we do not needRowAccumulatorcode anymoreThe
RowAccumulatorwere the last user of thedatafusion-rowcrate -- we now fully use the upstreamarrow_rowcrate https://docs.rs/arrow-row/43.0.0/arrow_row/index.htmlWhat changes are included in this PR?
RowAccumulatorsdatafusion-rowcrateAre these changes tested?
existing coverage
Are there any user-facing changes?
No