Move config.h include from st.c to x.c

config.h includes references to KeySyms and other X stuff.  Until we
come up with a cleaner way to separate configuration, it is simpler
(leads to more code removal) to have this here.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

win.h

@@ -18,6 +18,3 @@ void xsettitle(char *);
 void xsetpointermotion(int);
 void xselpaste(void);
 void xsetsel(char *, Time);
-void zoom(const Arg *);
-void zoomabs(const Arg *);
-void zoomreset(const Arg *);