removeByKey method
Remove a specific associated 'StateXController' from this StateX object by using its unique 'key' identifier.
Implementation
bool removeByKey(String keyId) {
final con = _mapControllers[keyId];
final there = con != null;
if (there) {
con._popStateFromSetter(_stateX);
_mapControllers.remove(keyId);
}
return there;
}