Does not work with async files

Hi, I tried to implement it in my project and ran into a problem. Async components do not correctly handle and delete styles.

An error occurs during the build
`WARNING: Stray reference to block import (styles). Imports are removed during rewrite so this will probably be a runtime error. (/Users/a.marchenko/Downloads/css-blocks-async/src/Strong.jsx:7:28)`

When you run the error
`ReferenceError: styles is not defined`

Example repo - https://github.com/Tom910/css-blocks-async-broken

Start with the linked css-blocks-async-broken example and reproduce the build warning at Strong.jsx:7:28, then trace why the async component's styles reference is removed. Done means async components handle and delete styles without the stray block-import warning or the resulting ReferenceError.

Written by the indexing model from the issue text.