voicemail notification settings cleanup

- remove UI preference for voicemail notification ringtone & vibration
settings as they are not functioning with notification channel
introduced
- have a new Notification Preference under voicemailSettings which will
navigate to the system settings screen for that channel.
- modify telephonymanager API getVoiceMailRingToneUri and
isVoiceMailVibrationEnabled from sharedPreference to NotificationChannel
data.
- more cleanup work needed till next API bump for telephonyManager APIs
setVoicemailVibrationEnabled and setVoicemailRingToneUri

Bug: 37912316
Test: Manaul test
Change-Id: Ic28713c012672b991b8f131545c06e1dbfd6765f