Bluetooth: Remove unused hci-destruct cb

The hci-destruct callback is not used by any driver so we can remove it.
There is no reason to keep it alive, anymore. Drivers can free their
internal data on driver-release and we do not need to provide a public
destruct callback.

Internally, we still use a destruct callback inside of hci_sysfs.c. This
one is used to correctly free our hci_dev data structure if no more
users have a reference to it.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>