Reverts apache/incubator-doris#7351 This commit will cause wrong result with agg table. For example, an agg table `(k1, k2, v1 sum)` with single non-overlapping rowset `select count(k1) from tbl1;` should using `_direct_agg_key_next_row` instead of `_agg_key_next_row`. Otherwise it return less rows than expected.(because `_agg_key_next_row` will only do aggregation with `k1`)