Revert "Cleanup IO buffers after opening the serial port"

We had reports that the first lines received via serial are lost.
This happens in particular on devices with fast native USB serial port.

This reverts commit c28e1a0.

Author: cmaglie

main.go

@@ -161,11 +161,6 @@ func (d *SerialMonitor) Open(boardPort string) (io.ReadWriter, error) {
 	if err != nil {
 		return nil, err
 	}
-
-	// Clean up residual data in IO buffers
-	_ = serialPort.ResetInputBuffer() // do not error if resetting buffers fails
-	_ = serialPort.ResetOutputBuffer()
-
 	d.openedPort = true
 	d.serialPort = serialPort
 	return d.serialPort, nil