Redo environment files as .txt instead of YAML

[scottstanie]

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[scottstanie]

Closing this after doing more dependency analysis- apparently removing only isce3 from the required dependencies leads to just 6 fewer lines in the conda specfile. Still including GDAL means that the majority of the large list remains, so it doesn't give a noticeable speedup to the environment solving or to the docker creation.

If we refactor further so that GDAL is also optional, then it'll be worth decoupling the isce dependencies. Until then, it seems like making unwrapping dependencies optional could be more trouble than benefit.