Consider if measurement data comes from vmux pad or internal ADC
Soon we will implement an option in all measurement scripts to read vmux values from internal ADC instead of the vmux pad (see module-qc-tools#20 (closed)). Once this is implemented, we need to update our analysis to take this into account. If the measurements were performed with the vmux pad, then we need to perform ground subtraction as we do now. If the internal ADC is used, then we should not subtract ground anymore.