removeListener method
remove the listener used for notify the data source changes.
Stop calling the listener every time the the collection in CalendarDataSource changed.
If listener
is not currently registered as a listener, this method does
nothing.
Listeners can be added with addListener.
Implementation
void removeListener(CalendarDataSourceCallback listener) {
if (_listeners == null) {
return;
}
_listeners!.remove(listener);
}