removeElement method
Removes element from this instance.
Implementation
@override
bool removeElement(PCanvasElement2D element) {
  var rm = _elements.remove(element);
  if (rm) {
    element.parent = null;
  }
  return rm;
}Removes element from this instance.
@override
bool removeElement(PCanvasElement2D element) {
  var rm = _elements.remove(element);
  if (rm) {
    element.parent = null;
  }
  return rm;
}