[iOS] Remove specific animation by key instead of removing all. If we don' t remove, updating transform won't work after doing CAAnimation. http://dotwe.org/vue/ce7d8d3bd4e67d3fe321c9e8b0bbbb7b (#1734)

Author: wqyfavor

ios/sdk/WeexSDK/Sources/Module/WXAnimationModule.m

@@ -123,7 +123,7 @@ - (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag
         _animationInfo.target.view.layer.anchorPoint = _animationInfo.originAnchorPoint;
         _animationInfo.target.view.layer.frame = originFrame;
     }
-    [_animationInfo.target.layer removeAllAnimations];
+    [_animationInfo.target.layer removeAnimationForKey:_animationInfo.propertyName];
 
     if (_finishBlock) {
         _finishBlock(flag);