[Settings] Replace ImsManager#isWfcEnabledByPlatform()

Replace ImsManager#isWfcEnabledByPlatform().

Bug:  140542283
Test: m RunSettingsRoboTests -j
ROBOTEST_FILTER=WifiCallingSettingsForSubTest
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=WifiCallingSettingsTest
Test: m RunSettingsRoboTests -j
ROBOTEST_FILTER=WifiCallingPreferenceControllerTest

Change-Id: I85907efb39aecdb3fb18cacf11ce4510b898edc4
4 files changed