pkt_sched: sch_qfq: remove redundant -if- control statement

The control !hlist_unhashed() in qfq_destroy_agg() is unnecessary
because already performed in hlist_del_init(), so remove it.

Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>