net: cdc_ncm: remove probe and disconnect wrappers

These functions were merely wrappers around the usbnet
variants.  Remove them.

Cc: Alexey Orishko <alexey.orishko@gmail.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>