Input: synaptics - remove X250 from the topbuttonpad list

Lenovo X250 has a PnpID of LEN0046, but it does not have the top software
button requirement.

For the record, Lenovo T450s and W541 have a PnpID of LEN200f and LEN004a,
so they are not on the top software button list.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Daniel Martin <consume.noise@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>