Remove leftover mentions of scat_species_XXX_field

[olemke]

Question @m-brath, @erikssonpatrick : I've removed some leftover mentions of scat_species_XXX_field in methods.cc, but I'm struggling with the documentation for cloudboxSetAutomatically. It also refers to scat_species_XXX_field in several sentences. I'm especially unsure how to correct the second paragraph that ends with:

For the latter, the WSM needs to be called once per each scat_species_XXX_field, with previously determined cloudbox_limits provided through cloudbox_limits_old.

Does "the latter" here refer explicitly to scat_species_XXX_field and if so, does that mean that cloudbox_limits_old has no use anymore?

[erikssonpatrick]

Seems that the WSM is still using the old PSD system, so I have to refer to @m-brath.

However, I would say that the text here is not critical for v2.4, but the WSM and its text should be updated to v3 as part inside issue #206.

In line with what I write for CHANGES, the question is if we bother to document all around the old PSD system, as we plan to remove it.

[olemke]

Updated docs for cloudboxSetAutomatically after discussion with @m-brath