Replace ADCChannel.ReadTemperature() with a simple ReadTemperature
function.
Not all chips will have a temperature sensor that is read by sampling an
ADC channel. The replacement ReadTemperature is simpler and more generic
to other chip families.
This breaks chips that were relying on the previous ReadTemperature
method. I hope it won't break a lot of existing code. If it does, a
fallback can be added.
Do it all at once in preparation for Go 1.18 support.
To make this commit, I've simply modified the `fmt-check` Makefile
target to rewrite files instead of listing the differences. So this is a
fully mechanical change, it should not have introduced any errors.
