netgraph/ng_bridge: Remove old table ABI

This was announced to happen after the 12 relases.
Remove a depeciated ABI.

The complete removal is for HEAD only. I'll remove the #define in
stable/13 as MFC, so the code will still exist in 13.x, but will not
included by default. Earlier versions will not be affected.

Reviewed by: kp
MFC after: 5 days
Differential Revision: https://reviews.freebsd.org/D28518