[Settings] replace isNonTtyOrTtyOnVolteEnabled() and isVtEnabledByUser() in VT

1. Code refactor
2. Replace ImsManager#isNonTtyOrTtyOnVolteEnabled() by combination of
   TelecomManager#getCurrentTtyMode() and
   ImsMmTelManager#isTtyOverVolteEnabled()
3. Replace ImsManager#isVtEnabledByUser() by
ImsMmTelManager#isVtSettingEnabled()

Bug: 140542283
Test: m RunSettingsRoboTests -j
ROBOTEST_FILTER=VideoCallingPreferenceControllerTest

Change-Id: I731c086cfea4330424b042bbf473b3cf77696a8c