Yank crufty INTR_FILTER option

It was introduced to the tree in r169320 and r169321 in May 2007.

It never got much use and never became a kernel default. The code
duplicates the default path quite a bit, with slight modifications. Just
yank out the cruft. Whatever goals were being aimed for can probably be met
within the existing framework, without a flag day option.

Mostly mechanical change: 'unifdef -m -UINTR_FILTER'.

Reviewed by: mmacy
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D15546