expression/aggregation: remove unused function in `aggregation.Aggregation` (#8608)
expression/aggregation: remove unused function in `aggregation.Aggregation` (#8608)


EvilMcJerkface/tidb,pingcap/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,Cofyc/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,coocood/tidb,ming-relax/tidb,qiuyesuifeng/tidb,ngaut/tidb,XuHuaiyu/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,XuHuaiyu/tidb,kyle-wang/tidb,coocood/tidb,pingcap/tidb,ngaut/tidb,qiuyesuifeng/tidb,ngaut/tidb,ming-relax/tidb,ngaut/tidb,cosmtrek/tidb,pingcap/tidb,cosmtrek/tidb,Cofyc/tidb,kyle-wang/tidb,ngaut/tidb