w1: remove ds1wm driver

This driver was used by the mfd/asic3 and mfd/htc-pasic3 drivers, but
both of those are removed as part of the PXA spring cleaning, which
leaves the w1 support orphaned as well.

Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Szabolcs Gyurko <szabolcs.gyurko@tlt.hu>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>