V4L/DVB (13476): spec: remove old dvb-spec and v4l2-spec directories

It was really confusing to have media-specs, v4l2-spec and dvb-spec.
So this patch removes v4l2-spec and dvb-spec. The docs in dvb-spec and
the V4L1_API.html file were moved to media-specs/old-docs.

Removed all references to v4l2-spec and dvb-spec.

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