Remove .columns file dependence

[sschmidt23]

Having to read in a few numbers from a .columns file rather than via a config param is annoying, and a remnant of how DESC_BPZ does things. It should be simple to remove the one or two things that are read from .columns and instead make those config params.

[sschmidt23]

Looking at the code, it's even less involved than I thought, I thought that we read the names of the mags, mag_errs, and zp_offsets from the columns file, but I already moved those to config params, the only remaining thing in the .columns is the filter names, should be trivial to move that to a config param.