Bluetooth: Simplify use of hci_pend_le_conns_clear()

Now that pend_le_connections is a list of hci_conn_params entries we can
simply remove items from that list as we iterate through the global list
of le_conn_params. This also moves the responsibility of calling
hci_update_background_scan() to the functions that were previously
calling hci_pend_le_conns_clear(). The only user that's left for
hci_pend_le_conns_clear() is hci_dev_do_close() which anyway does not
need to call hci_update_background_scan().

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>