dix: remove some obsolete comment.

The "counterpart to biggest hack" included checking for the motion history
function - which is unified in 1.7. Hence the check (which is already
removed) would evaluate to true anyway, and this comment isn't needed.

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

dix/devices.c

@@ -686,7 +686,6 @@ FreeDeviceClass(int type, pointer *class)
             {
                 ValuatorClassPtr *v = (ValuatorClassPtr*)class;
 
-                /* Counterpart to 'biggest hack ever' in init. */
                 if ((*v)->motion)
                     xfree((*v)->motion);
                 xfree((*v));