Input: wacom_w8001 - drop use of ABS_MT_TOOL_TYPE

As of e0361b70

 ("Input: wacom_w8001 - split the touch and pen devices
into two devices") the touch events aren't multiplexed over the same device
anymore, the use of ABS_MT_TOOL_TYPE is superfluous. And even before then
it only ever sent MT_TOOL_TYPE_FINGER anyway.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>