The member (u32) "num_active_agg" of struct qfq_sched has been unused
since its introduction in 462dbc9101acd38e92eda93c0726857517a24bbd
"pkt_sched: QFQ Plus: fair-queueing service at DRR cost" and (AFAICT)
there is no active plan to use it; this removes the member.