message: Fix warnings in JSON.cpp, NFC
  These asserts are no-ops, and are supplanted by -Wcovered-switch.
diff: @@ -58,7 +58,6 @@ uint64_t JSONNumber::GetAsUnsigned() const {
  case DataType::Double:
  return (uint64_t)m_data.m_double;
  }
  - assert("Unhandled data type");
  }
  int64_t JSONNumber::GetAsSigned() const {
  @@ -70,7 +69,6 @@ int64_t JSONNumber::GetAsSigned() const {
  case DataType::Double:
  return (int64_t)m_data.m_double;
  }
  - assert("Unhandled data type");
  }
  double JSONNumber::GetAsDouble() const {
  @@ -82,7 +80,6 @@ double JSONNumber::GetAsDouble() const {
  case DataType::Double:
  return m_data.m_double;
  }
  - assert("Unhandled data type");
  }
  void JSONNumber::Write(std::ostream &s) {
  