net_sched: netem: remove qdisc_is_throttled() use

Looks like it is only there as some optimization attempt.

Since __QDISC_STATE_THROTTLED set/unset is way too expensive,
and netem is the last user, just remove this check.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>