Change `-W help` to display edition level.
`-W help` was not honoring the `--edition` flag when displaying the default lint level. It was using the edition for sorting, but not for the final display.
This isn't important right now as there aren't any edition-specific lint levels. Also, the `declare_lint` macro is broken and doesn't even allow setting them right now. However, I figure it wouldn't hurt to fix this before I forget about it, in case edition-specific lints are ever used in the future.
2b53ec3d1e