net: ethernet: ti: netcp_core: no need in netif_napi_del

Don't remove rx_napi specifically just before free_netdev(),
it's supposed to be done in it and is confusing w/o tx_napi deletion.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>