media: Documentation: mc: Replace deprecated graph walk API

media: Documentation: mc: Replace deprecated graph walk API

The graph walk API has been deprecated in commit eac564de0915 ("media:
mc: entity: Add entity iterator for media_pipeline") in favour of
pipelien iterators, but the MC documentation hasn't been updated
accordingly. It still documents the deprecated API as the only option.
Fix it by dropping the deprecated function, and documenting the new API.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://lore.kernel.org/r/20240822212445.2037-5-laurent.pinchart+renesas@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>