dix: reduce FirstPointerChild complexity

Instead of keeping a flag on each window for the devices that are in this
window, keep a local array that holds the current pointer window for each
device. Benefit: searching for the first descendant of a pointer is a simple
run through the array.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

include/windowstr.h

@@ -183,7 +183,6 @@ typedef struct _Window {
      * FocusIn/Out events for multiple pointers/keyboards. Each device ID
      * corresponds to one bit. If set, the device is in the window/has focus.
      */
-    char                enterleave[(MAXDEVICES + 7)/8];
     char                focusinout[(MAXDEVICES + 7)/8];
 } WindowRec;