Remove X and fontconfig from st.c

None of the X-related includes are needed any longer.  In addition, move
the X modifier defines into x.c, as they are not used outside.

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

x.c

@@ -44,6 +44,11 @@ typedef struct {
 	signed char crlf;      /* crlf mode          */
 } Key;
 
+/* X modifiers */
+#define XK_ANY_MOD    UINT_MAX
+#define XK_NO_MOD     0
+#define XK_SWITCH_MOD (1<<13)
+
 /* function definitions used in config.h */
 static void clipcopy(const Arg *);
 static void clippaste(const Arg *);