Improve documentation and readability of ai_remove_ship_goal()
Ensure all occurences of ai_info resetting or clearing goals use the in place template function, rather than rolling their own. This should ensure subsequently refactors do not miss the (presently) duplicated code in other locations.
Ensure all occurences of resetting an ai_goals structure use a templated form. This will improve readability, and should AI code be refactored will reduce the likelihood of (presently) duplicated code being missed.