media: v4l2-dev.h: remove VFL_TYPE_GRABBER

The last driver was converted to use VFL_TYPE_VIDEO, so the old
_GRABBER enum can now be removed.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>