HID: multitouch: remove pen special handling

Pens have a special handling in hid-mt as hybrid pen/touch devices
are quite common now. However, some fancy devices presents also
useful collections like mouse or keyboard.
The special case for the pen may not be a special case, and treat it as
a generic case.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>