devlink: remove devl*_port_health_reporter_destroy()

Remove port-specific health reporter destroy function as it is
currently the same as the instance one so no longer needed. Inline
__devlink_health_reporter_destroy() as it is no longer called from
multiple places.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>