Flush now uses ftdi_tcioflush() when libftdi ≥ 1.5.

When libftdi version 1.5 is available, it is recommended to use replaced flush functions.

Below is from https://www.intra2net.com/en/developer/libftdi/
Implement tc[io]flush methods & deprecate broken purge_buffers methods
Please check your code for ftdi_usb_purge_rx_buffer(), ftdi_usb_purge_tx_buffer() and ftdi_usb_purge_buffers() and migrate to the new ftdi_tc[io]flush() methods.