xkbcli-compose: Simplify locale options Current options to set the locale are convoluted: - An explicit locale *must* be given, while a sane default would be to use the user environment. - Then there are two options that were useful while testing locale handling: read environment variables or use `setlocale`. But the program has already called: ``` setlocale(LC_ALL, ""); ``` so it turns out the two options lead to the same results. Remove options `--locale-from-env` and `--locale-from-setlocale` and make the locale default to the user environment.