The xinerama related variables in config.mk are a relict of
dwm and therefore should be removed.

Proprietary UNIX variants like AIX, HP-UX or SCO UNIX
are nowadays rarely used and maintaining compatibility to
non-standard operating systems interfaces is wasteful and
practically useless.

Projects like xterm suffer from backward compatibility to decades-old
UNIX variants and terminal standards. This does not conform to st's
design goals.