[P1] Enable linting for ESLint override files

[willroberts]

We have several files with overrides set in .eslintrc.json:

    {
      "files": ["app/**/*.js"],
      "rules": {"camelcase": ["warn"]}
    },
    {
      "files": ["test/**/*.js"],
      "rules": {"no-unused-expressions": ["off"]}
    }

We should remove these overrides and resolve the underlying linting issues.

[adam-jennings]

It looks like the list of overrides has grown a little bit. I'd like to take on this issue and help resolve the linting issues