V4L/DVB (8689): dpc7146: remove dpc7146 demonstration board driver

Old driver for the dpc7146 demonstration board that is no longer
relevant. The last time this was tested on actual hardware was
probably around 2002. Since this is a driver for a demonstration
board the decision was made (after discussing this with the original
author, Michael Hunold) to remove it rather than spending a
lot of effort continually updating this driver to stay in sync
with the latest internal V4L2 or I2C API.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Michael Hunold <hunold@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>