Both the .json and .yml config formats are deprecated in favor of flat configs exported from eslint.config.js files. The good news is that gjs' config is now available as a shared config from the `eslint-config-gnome` package in World/javascript, so we no longer have to copy the entire thing. Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/408>