Clean up EPICS channel numbering for storing reference model values

I propose we do not try to maintain backwards compatibility as we move towards O4 with EPICS channel numbering (EPXX) and its correspondence to reference model values. Some of these EPXX channels are deprecated and we will likely need new ones in O4 for exact TDCF calculations. We should determine all that is needed and develop new labels for O4 to be used consistently across pyDARM, CALCS and gstlal-calibration.