codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()

After making all ->qlen_notify() callbacks idempotent, now it is safe to
remove the check of qlen!=0 from both fq_codel_dequeue() and
codel_qdisc_dequeue().

Reported-by: Gerrard Tai <gerrard.tai@starlabs.sg>
Fixes: 4b549a2e ("fq_codel: Fair Queue Codel AQM")
Fixes: 76e3cc12 ("codel: Controlled Delay AQM")
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250403211636.166257-1-xiyou.wangcong@gmail.com


Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>