net/sched/sch_hfsc.c: remove leftover dlist and droplist

This is update to:
commit a09ceb0e ("sched: remove qdisc->drop")

That commit removed qdisc->drop, but left alone dlist and droplist
that no longer serve any meaningful purpose.

Signed-off-by: Michal Soltys <soltys@ziu.info>
Signed-off-by: David S. Miller <davem@davemloft.net>