No need to use cfg_attr and have to worry about syncing the preconditions for the cfg_attr with the preconditions for where `slice_contains_slice()` is used in the codebase, just mark it as `allow(unused)` with a comment.
Remove unnecessary L!
There are a bunch more now that widestrs is gone
This removes both the `#[widestrs]` annotation as well as all `"foo"L` suffixes, and does a `cargo fmt` run on the result
