Dynamically removes all event sources, or multiple specific event sources.
.fullCalendar( ‘removeEventSources’, optionalSourcesArray )
optionalSourcesArray is not given, all event sources will be removed.
optionalSourcesArray parameter is an array of identifier items, which can be either an event source’s id/Array/URL/Function or the full Event Source Object.
Events from the specified sources will be immediately removed from the calendar, resulting in a single re-rendering.