Bluetooth: Remove LE scan helpers

This patch removes the LE scan helpers hci_le_scan and hci_cancel_
le_scan and all code related to it. We now use the HCI request
framework in device discovery functionality and these helpers are
no longer needed.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>