Replace pysynphot with synphot

pysyphot is not longer supported:
https://github.com/spacetelescope/pysynphot/blob/master/ROADMAP.md

We should replace with synphot. 
https://github.com/spacetelescope/synphot_refactor/

There is a map between the old and new functionality here:
https://synphot.readthedocs.io/en/latest/synphot/from_pysyn_iraf.html

Requires python 3.10 and later. 