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