If XTest is always required, then eliminate the XTest devPrivate

The internals of XTest are used by Xi and Xkb, and both Xi and Xkb are
always required, so it makes little sense to have XTest place data in
a devPrivate, especially a devPrivate which is only available when the
XTest extension is enabled.

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

include/inputstr.h

@@ -554,6 +554,9 @@ typedef struct _DeviceIntRec {
 
     /* coordinate transformation matrix for absolute input devices */
     struct pixman_f_transform transform;
+
+    /* XTest related master device id */
+    int xtest_master_id;
 } DeviceIntRec;
 
 typedef struct {