Called when this panel is removed from Frontend.panels, preventing it from being shown in the system UI.

This may be called as a result of dismissing the panel, or due to other factors such as the frontend deciding that the panel is no longer relevant.

Be sure not to trigger new asynchronous calls that depend on this panel's lifecycle when overriding this method. E.g., IVI service calls. The panel's lifecycle will be destroyed here and the calls might not be processed.