Fix memory leak when GUI window is closed (RustAudio#198)

Author: Quant1um

src/gl/macos.rs

@@ -91,7 +91,6 @@ impl GlContext {
 
         view.setWantsBestResolutionOpenGLSurface_(YES);
 
-        let () = msg_send![view, retain];
         NSOpenGLView::display_(view);
         parent_view.addSubview_(view);