ieee802154: Remove ieee802154_reduced_mlme_ops references.

As there doesn't seem to be a definition of it or any users of it.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>