function unload(filenames, options = {}) {
  const parsed = parse(filenames, options);

  Object.keys(parsed).forEach((key) => {
    if (process.env[key] === parsed[key]) {
      delete process.env[key];
    }
  });
}
Unload variables defined in a given file(s) from `process.env`.

This function can gracefully resolve the following issue:

In some cases, the original "dotenv" library can be used by one of the dependent npm modules.
It causes calling the original `dotenv.config()` that loads the `.env` file from your project before you can call `dotenv-flow.config()`.
Such cases break `.env*` files priority because the previously loaded environment variables are treated as shell-defined thus having a higher priority.

Unloading the previously loaded `.env` file can be activated when using the `dotenv-flow.config()` with the `purge_dotenv` option set to `true`.

@param {string|string[]} filenames - filename or a list of filenames to unload
@param {object} [options] - `fs.readFileSync` options