Empty objects from extended configurations are added to output ESLint configurations

[JoshuaKGoldberg]

🐛 Bug Report

• tslint-to-eslint-config version: 1.0.0-beta
• ESLint version: 7.0.0
• Node version: 12.4.0

Actual Behavior

See comment in #448 (comment): if you run tslint-to-eslint-config twice, it looks like some config values are getting picked up from extended configs.

    // ...
    "ignorePatterns": [],
    // ...

Expected Behavior

Don't add those things. Do not want.

Reproduction

With a tslint.json that contains { extends: "tslint:recommended" }:

npx tslint-to-eslint-config
npx tslint-to-eslint-config