Unused compiled CSS classes aren't eliminated

As titled. In the example below you can see that unused styles are bundled- I'd expect that rollup is able to remove them in context of `CSS-Modules`.

```jsx
var styles = {"button":"Button__button","unused":"Button__unused"};

// eslint-disable-next-line no-unused-vars
function Button() {
return /*#__PURE__*/React.createElement("div", {
className: styles.button
});
}

export default Button;

```