Clean up prelude-coffee.el

- `coffee-js-mode` and `coffee-debug-mode` is not used by coffee-mode, the default `coffee-command` is  already "coffee"
- Of course we want the compiled file to be wrapped, it's the best practice of JavaScript and it's why we use CoffeeScript in the first place.
- `coffee-compile-buffer` is already bound to <kbd>C-c C-k</kbd>