WifiScanner: Change hidden/PNO scan params

Since networks are no longer configured in wpa_supplicant, network
IDs/priorities being passed around for hidden/PNO scanning does not
make any sense.
Changing the wifi scanner interface to remove all network ID/priority
references. These will be replaced by SSID of the corresponding
networks for hidden networks.

BUG: 29503772
TEST: Existing unit tests.
TEST: Successfully connected to a hidden network on device
Change-Id: I5d877e0345d574fb513b6eecca14f65f2ee4e7ab