It's not "needed" or "unneeded", it's just "required for the Caravel ML-SoC test chip". As indicated, all rows that have corresponding pages with specifications are in play for the challenge, which is rows 5 to 24. For rows 23 and 24, we currently don't have a plan to put them on the June tapeout, but if a finished IP block is available, we'll probably fit it in somewhere.