code: func (b *BoxLayout) RemoveWidget(widget Widget) {
  	changed := false
  	for i := 0; i < len(b.cells); i++ {
  		if b.cells[i].widget == widget {
  			b.cells = append(b.cells[:i], b.cells[i+1:]...)
  			changed = true
  		}
  	}
  	if !changed {
  		return
  	}
  	b.changed = true
  	widget.Unwatch(b)
  	b.layout()
  	b.PostEventWidgetContent(b)
  }
docs: // RemoveWidget removes a Widget from the layout.