Remove more remnants of ng_fec(4).

The ng_create_one() and ng_mkpeer() functions in network.subr are
now not used anywhere, but I left them, since they can be useful
in future in netgraph scripting.

Submitted by:	pluknet
repair build for dev/cs.

Reported by: Outback Dingo <outbackdingo@gmail.com>
[automated] Merge in upstream-github/master