software node: Remove unused APIs

There are no more users of software_node_register_nodes() and
software_node_unregister_nodes(). Remove them.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Daniel Scally <dan.scally@ideasonboard.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20221228094922.84119-5-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>