ipfilter: Remove unused ioctl

The SIOCSTAT1 ioctl is only used in ip_auth and is unused in ip_state.
The ip_state version was likely added to support a new statistic yet
to be developed in ipfstat(8) or for some sample userspace application
(similar in fashion to the sample provided for authentication rules).
There is no need to report individual state hash table bucket lengths
to any future userspace application.

If needed for any future debugging purposes a DTrace probe would be a
better vehicle.

This unused ioctl in ip_stat results in a panic.

PR: 266124
Reported by: Robert Morris <rtm@lcs.mit.edu>
MFC after: 3 days