Use new WifiSsid creator methods in unit tests

Use the new WifiSsid.fromString() instead of
WifiSsid.createFromAsciiEncoded() in SettingsLib tests and
WifiNetworkScoreCacheTest

Bug: 136480579
Test: atest AccessPointTest WifiTrackerTest WifiNetworkScoreCacheTest
Change-Id: Ic8d862d24626da73fe1664b871f4412e700ce666
3 files changed