message: Remove unused extern near _write
diff: #define UART_TX_BUFFER_SIZE 64
  static uint8_t uart_tx_buf[UART_TX_BUFFER_SIZE];
  -extern PCD_HandleTypeDef hpcd_USB_OTG_FS;
  extern USBD_HandleTypeDef hUsbDeviceFS;
  int _write(int file, char* data, int len) {
  