Review the lists/ folder and clean out anything unused

[andymeneely]

The lists/ folder in this repo has gotten more bloated than I had expected. I'd like someone to go through it and clean out anything that is not being used by an existing script. Search for the name in the scripts.

Also, if it's an intermediate file that is easily regenerated from others, we can delete that too.

Lastly, write a README.md file in lists/ that explains each file and what script uses it.

The purpose of lists/ is to have manually-curated lists of things that we need. For example, c_repos.txt is the list of repositories that primarily have the programming language C that we use for a study.

[KaitlinYandik]

I can take this on if nobody else is interested?