Fix image source prop change updating image

Summary:
fixes #7795
fixes #8500

Motivation: When having a simple button that changes the Image source when tapped, the image doesn't change (or at least sometimes, intermittently it works).

This was found to be an issue where the request was being sent to the native layer correctly but then being subsequently cancelled by the `reactSetFrame: method`  ...
Closes https://github.com/facebook/react-native/pull/9137

Differential Revision: D3702867

Pulled By: javache

fbshipit-source-id: c89ce6b841179394b6b23850b3128751ef9e0313

Libraries/Image/RCTImageView.m

@@ -358,10 +358,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
         _targetSize = idealSize;
         [self reloadImage];
       }
-    } else {
-      // Our existing image is good enough.
-      [self cancelImageLoad];
-      _targetSize = imageSize;
     }
   }
 }