Update OnlineHelper#concurrentDML to correctly transform row types

With the new Row/RowType code in the write branch, DDL changes modify RowTypes enough so assert checks for `typea == typeb` are no longer correct. The concurrenDML processing, which is supposed to handle this, now does again properly. 

This change allows the OnlineCreateTable*MT and OnlineCreateGroupIndex*MT tests to pass correctly again.