devlink: remove duplicate temporary netlink callback prototypes

Remove the duplicate temporary netlink callback prototype as the
generated ones are already in place.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230811155714.1736405-9-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>