BasicEventManager : object
Note that this has no effect on the current event execution - this simply prevents the event from receiving additional notifications in the future.
This is provided mostly as a convenience for cases where an event is known to be uniquely identifiable by its object and property values; this saves the caller the trouble of keeping track of the Event object created when the event was first registered.
When a particular object/property combination might be used in several different events, it's better to keep a reference to the Event object representing each event, and use removeEvent() to remove the specific Event object of interest.
Returns true if we find any matching events, nil if not.