Cleanup: PhoneNumberUtils.isVoicemailNumber is now public.

This code isn't needed anymore (?). It seems to follow a very similar
codepath, except for this uses extractNetworkPortion instead of
extractNetworkPortionAlt. I think it seems safe enough to cleanup?

Change-Id: I6b626fa7797ead5f5eeb9456589805694055f037
1 file changed