devlink: Delete not-used devlink APIs

Devlink core exported generously the functions calls that were used
by netdevsim tests or not used at all.

Delete such APIs with one exception - devlink_alloc_ns(). That function
should be spared from deleting because it is a special form of devlink_alloc()
needed for the netdevsim.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>