message: Migrate GetCancelled and GetUnknown to use the non-deprecated constructor.
  While it doesn't really matter, this reduces the number of warnings compiling Tink produces. (We could also deprecate the functions, but it doesn't matter...)
diff: @@ -34,13 +34,13 @@ namespace {
  const Status& GetCancelled() {
  static const Status* status =
  - new Status(::crypto::tink::util::error::CANCELLED, "");
  + new Status(absl::StatusCode::kCancelled, "");
  return *status;
  }
  const Status& GetUnknown() {
  static const Status* status =
  - new Status(::crypto::tink::util::error::UNKNOWN, "");
  + new Status(absl::StatusCode::kUnknown, "");
  return *status;
  }
  