Cancels the loading of all values for all observers.
- iOS 4.0+
- macOS 10.7+
- UIKit for Mac 13.0+Beta
- tvOS 9.0+
- watchOS 6.0+Beta
This method explicitly cancels any pending invocations of the asset’s
load method. This method should only be used when you are completely done using an asset and you want to terminate any outstanding requests. Deallocation of an instance of the asset implicitly invokes this method if any loading requests are still pending.