[media] cx25821: remove bogus radio/vbi/'video-ioctl' support

This device does not support radio or vbi, so remove anything referring
to that.
In addition, the driver created an 'video ioctl' node, which was unused and
was effectively identical to the first video node.
This bogus video node is now removed, leaving us with 8 video capture nodes
and 2 video output nodes.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>