Remove wrong information about fat arrow notation

The fat arrow isn't needed for object methods, and in fact CoffeeScript will generate exactly the same code as with a thin arrow - see [this part of the coffeescript code][https://github.com/jashkenas/coffee-script/blob/d687d52f9e36e093c73419d913c8cb6b1d062fd4/src/nodes.coffee#L1342]