Tells the view that a subview is about to be removed.
- iOS 2.0+
- Mac Catalyst 13.0+
- tvOS 9.0+
The subview that will be removed.
The default implementation of this method does nothing. Subclasses can override it to perform additional actions whenever subviews are removed. This method is called when the subview’s superview changes or when the subview is removed from the view hierarchy completely.