webbpsf.JWInstrument.calcPSF duplicates code from poppy.Instrument.calcPSF

[josePhoenix]

We should factor out the JWST-specific stuff where possible and call the superclass' calcPSF.

[josePhoenix]

@mperrin It looks like the only things that will change if I remove SpaceTelescopeInstrument.calcPSF entirely are:

• no more calc_oversample= argument to raise a deprecation warning (we said we would remove this in 0.4)
• no more filter= argument to override Instrument.filter -- I think this is a good change for consistency with poppy.Instrument, and I wasn't aware it was there

[mperrin]

I agree those are fine to remove. The other small detail (also OK to remove) is the code I added to set the default source spectrum to a 5700 K blackbody, to silence the warning or error that poppy.Instrument._getWeights would otherwise produce. The more I think about it, the less I think that should be a warning message, since it's such a common usage case for users to ask for a PSF without giving an explicit source spectrum.

So I would propose in poppy we convert that to a benign info message instead of a warning, and then there's no need for any code in webbpsf.Instrument to avoid triggering it. I think I may just go ahead and do that right now.

[mperrin]

This was fixed in #132. There is no longer a separate JWInstrument.calcPSF (nor calc_psf); it just uses the one in poppy.