Тут Xorg почистил кодовую базу: lists.x.org/archives/xorg-deve

lib/liboldX:
This provided backwards compatibility for apps from X Version 10, which
was the version of the X Window System from November 1985, replaced by
X11 in September 1987. 35 years seems like more than long enough to port
applications to using libX11 instead.

И ведь найдётся человек, который это использовал! :D