ndis(4): remove as previous announced

nids(4) was a clever idea in the early 2000's when the market was
flooded with 10/100 NICs with Windows-only drivers, but that hasn't been
the case for ages and the driver has had no meaningful maintenance in
ages. It only supports Windows-XP era drivers.

Also remove:

• ndis support from wpa_supplicant
• ndiscvt(8)

Reviewed By: emaste, bcr (manpages)
Differential Revision: https://reviews.freebsd.org/D27609