media: m2m-deinterlace: remove unused struct 'vb2_dc_conf'

'vb2_dc_conf' has been unused since the original
commit 8f0755c0 ("[media] media: Add mem2mem deinterlacing driver").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>