Revert workaround for rustfmt not being able to parse $crate

This was fixed in https://github.com/rust-lang/rust/issues/38016 so we can eventually get rid of [this workaround](https://github.com/dtolnay/cargo-expand/blob/0.3.4/src/main.rs#L51-L54).