media: ipu6: Remove redundant streaming start via buffer queueing

media: ipu6: Remove redundant streaming start via buffer queueing

The videobuf2 framework will ensure buffers are queued before streaming is
started. Remove support for starting streaming via the buf_queue()
callback.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Mehdi Djait <mehdi.djait@linux.intel.com> # Dell XPS 9315
Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>