Mainline: removed legacy UI for network selection mode.

Framework does not support getAvailableNetworks(), so legacy
UI does not work. Removed legacy UI for network selection mode.

Bug: 147404387
Test: 1.make RunSettingsRoboTests ROBOTEST_FILTER=\
NetworkScanHelperTest(PASS)
2.make RunSettingsRoboTests \
ROBOTEST_FILTER=NetworkSelectSettingsTest(PASS)
Change-Id: I421526e844100b08e0c39e6e993ca09d1fad8457