Bluetooth: Remove empty HCI event handlers

With the removal of hci_req_complete() several HCI event handlers have
essentially become empty and can be removed. The only potential benefit
of these could have been logging, but the hci_event, hci_cmd_complete
and hci_cmd_status already provide a log for events which they do not
have an explicit handler for.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>