This tool performs all calls client side, no keys will be saved. All calls are performed directly on the Github API. See source code here: https://github.com/jaap/github-deployment-cleaner
Based on https://stackblitz.com/edit/github-deployment-clearer And https://stackoverflow.com/questions/53452910/how-to-remove-a-github-environment
RECOMMENDED: Disconnect HEROKU from Github before doing this (though not strictly necessary, I think).
See https://stackoverflow.com/a/61272173/6569950 for more info.