Removes leftover TODO comment.

Refs #39.

Left in this comment while debugging the NodeJS v14+ issue with `@bazel/postcss` as one possible solution (#39 (comment)). Ultimately decided to stay on Node v12, so it's no longer relevant and there is nothing to do.

packages/rules_prerender/prerender_pages.bzl

@@ -149,7 +149,6 @@ def prerender_pages(
         postcss_binary(
             name = "%s_styles" % name,
             src = ":%s_styles.css" % prerender_name,
-            # TODO: Can remove this.
             sourcemap = True,
             output_name = bundled_css,
             plugins = {