Revert the style2str change in b547ead

The commit b547ead58bf09bb838c13f02afb2f1042ad1bc7c introduced change to `style2str`. I think it's wrong. Or at least I'd want to see a lot better justification for it then just changing inside unrelated patch.

In particular, there are no tests. As a maintainer of `cabal-plan` I want to understand the change, but I don't. So please revert it, and do it properly if there is justification.

Inspect commit b547ead and the history of `style2str` to understand the behavior change and why it was included in an unrelated patch. Compare the current implementation with its prior version, then confirm the intended behavior and whether tests should be added before reverting; completion means the unjustified change is removed or properly justified.

Written by the indexing model from the issue text.