HID: multitouch: Remove MT_CLS_WIN_8_DUAL

After commit c23e2043

 ("HID: multitouch: do not filter mice nodes"),
MT_CLS_WIN_8 also supports mouse nodes, hence make MT_CLS_WIN_8_DUAL
redundant.

Remove MT_CLS_WIN_8_DUAL accordingly.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>