Removed scary YAML parsing code, the function of which is to load from a user input...

Removed scary YAML parsing code, the function of which is to load from a user input string, except if the string has no line breaks in it, in which case an arbitrary local file/URL is loaded and handed to the attacker on a nicely encapsulated silver platter. Doesn't appear to be used either by core or extensions, but you never know when someone might try.