Removed DispatchWorkItemFlags implementation with async flags.
Removed DispatchWorkItemFlags implementation with async flags.

sessuru/AlamofireImage,daniele-pizziconi/AlamofireImage,Alamofire/AlamofireImage,Pluto-tv/AlamofireImage,daniele-pizziconi/AlamofireImage,sessuru/AlamofireImage,Alamofire/AlamofireImage,Pluto-tv/AlamofireImage