Bluetooth: remove unused member of hci_dev.

This patch removes core_data member from hci_dev struct as it is unused.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>