Remove redundant queue switch from RCTLocalAssetImageLoader

Summary:
Switching queues in `RCTLocalAssetImageLoader` is unnecessary. We dispatch to main queue before assigning the image to `UIImageView`.

Changelog: Remove redundant queue switch from RCTLocalAssetImageLoader

Reviewed By: PeteTheHeat

Differential Revision: D20347223

fbshipit-source-id: ff6215838f0462356d4a516e6ec31c82a742881a

Libraries/Image/RCTLocalAssetImageLoader.mm

@@ -49,12 +49,6 @@ RCT_EXPORT_MODULE()
                                  partialLoadHandler:(RCTImageLoaderPartialLoadBlock)partialLoadHandler
                                   completionHandler:(RCTImageLoaderCompletionBlock)completionHandler
 {
-  __block auto cancelled = std::make_shared<std::atomic<bool>>(false);
-  RCTExecuteOnMainQueue(^{
-    if (cancelled->load()) {
-      return;
-    }
-
   UIImage *image = RCTImageFromLocalAssetURL(imageURL);
   if (image) {
     if (progressHandler) {
@@ -66,11 +60,8 @@ RCT_EXPORT_MODULE()
     RCTLogWarn(@"%@", message);
     completionHandler(RCTErrorWithMessage(message), nil);
   }
-  });
   
-  return ^{
-    cancelled->store(true);
-  };
+  return nil;
 }
 
 @end