Allow for no analog anti-aliasing filter model to be given
This allows running in the configuration where no potentially no analog anti-aliasing filter is in a path (like sensing when using the new fast ADCs). I tried to also simplify the logic a little bit. There may be room for further improvement in a future merge request.
See: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=66992
Edited by Evan Goetz