Remove unused demod driver. Device that used it never went public.

If someone later decide to add support for a device using this
chipset, it should be easy enough to retrieve it from git
history.
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>