got rid of compile time xidx configuration, querying mouse pointer instead

config.def.h

@@ -13,10 +13,6 @@ static uint snap                    = 32;       /* snap pixel */
 static Bool showbar                 = True;     /* False means no bar */
 static Bool topbar                  = True;     /* False means bottom bar */
 
-#ifdef XINERAMA
-static uint xidx                    = 0;        /* Xinerama screen index to use */
-#endif
-
 /* tagging */
 static const char tags[][MAXTAGLEN] = { "1", "2", "3", "4", "5", "6", "7", "8", "9" };