8139too: Remove unnecessary netif_napi_del()

The call to free_netdev() in __rtl8139_cleanup_dev() clears the network device
napi list, and explicit calls to netif_napi_del() are unnecessary.

Signed-off-by: Bo Chen <chenbo@pdx.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>