media: v4l2-subdev: Remove g_pixelaspect operation

There are no consumers or implementations left in tree for the subdevice
operation g_pixelaspect, delete it.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250705083741.77517-4-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>