dmx: don't include dmx-config.h from xdmxconfig (#37502)

dmx: don't include dmx-config.h from xdmxconfig (#37502)

dmx-config.h is a server header which includes dix-config.h. That again
defines a bunch of server-specifics, including setting the size of XID to
32 bit.

libX11 uses unsigned long (8 bits on x86_64). XGCValues thus ends up being
16 bytes smaller in xdmxconfig than in the library, causing garbage to be
sent to the server.

X.Org Bug 37502 <http://bugs.freedesktop.org/show_bug.cgi?id=37502>

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>