Remove hidden @NetworkType in NetworkInfo

The NetworkType annotation is a hidden telephony symbol, and should be
kept hidden as annotations are disallowed by API guidelines.

Remove its usage in NetworkInfo as users of annotated constants that
build against API stubs are expected not to use the annotation.

Bug: 182451544
Test: m
Change-Id: I6658c1faa147c527c989b87d67f1af166c488dde