Migrate off deprecated getSourceKind and getResolvedLibrary (#2635)
Migrate off deprecated getSourceKind and getResolvedLibrary (#2635)

* Fix deprecated interface usage

* Strip some unnecessary checks from package_builder.
dart-lang/dartdoc,keertip/dartdoc,keertip/dartdoc,keertip/dartdoc,keertip/dartdoc,dart-lang/dartdoc,dart-lang/dartdoc,dart-lang/dartdoc