Simplify remote temperature calculation

[chwdt]

This PR simplifies and corrects calculation of temperature values in sendRemoteTemperature():

The original values calculated are:

packet[7] = 3 + ((round(temperature * 2) / 2) - 10) * 2
packet[8] = round(temperature * 2) / 2 * 2 + 128

which can be simplified to:

packet[7] = round(temperature * 2) - 17
packet[8] = round(temperature * 2) + 128

The heat pump ignores the value in packet[7] when packet[8] is set. Leaving packet[8] unset shows an error of 0.5°C between reported room temperature and sent remote temperature. Therefore the correct value should be:

packet[7] = round(temperature * 2) - 16