connector: remove redundant input callback from cn_dev

A small cleanup: this callback is never used.
Originally fixed by Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
for OpenVZ7 bug OVZ-6877

cc: stanislav.kinsburskiy@gmail.com
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>