Bluetooth: hci_request: Remove bg_scan_update work

This work is no longer necessary since all the code using it has been
converted to use hci_passive_scan/hci_passive_scan_sync.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>