net/mlx4_en: remove napi_hash_del() call

There is no need calling napi_hash_del()+synchronize_rcu() before
calling netif_napi_del()

netif_napi_del() does this already.

Using napi_hash_del() in a driver is useful only when dealing with
a batch of NAPI structures, so that a single synchronize_rcu() can
be used. mlx4_en_deactivate_cq() is deactivating a single NAPI.

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