XBOX/i386 and xlint removal

Hello,
I created two reviews to axe two features which I personally find of
little use in modern FreeBSD.

https://reviews.freebsd.org/D13015 xlint
https://reviews.freebsd.org/D13016 XBOX/i386

Reviews contain the explanations.  For xlint it is just an overdue, IMO.
While for XBOX I do not have much opposition against supporting the
obsoleted platforms, but the way the port was done pollutes the sources
with too much #ifdefs.  Since people often do not want to care about i386
together with amd64, additional hurdle only makes the things worse.

Feel free to add yourself as reviewer.  I intend to commit the patches
in a week, unless strong objections expressed by the time.