`[RCTShadowView localData]` is now only setter.

Summary: It saves 8 bytes per shadowView instance, and it is more logical because it does nothing by default.

Reviewed By: javache

Differential Revision: D5997804

fbshipit-source-id: c985a11aeea881e95911469e10c8c27429a2718a

React/Views/RCTShadowView.h

@@ -68,7 +68,7 @@ typedef void (^RCTApplierBlock)(NSDictionary<NSNumber *, UIView *> *viewRegistry
  * Use `-[RCTUIManager setLocalData:forView:]` to set this property
  * (to provide local/environmental data for a shadow view) from the main thread.
  */
-@property (nonatomic, strong) NSObject *localData;
+- (void)setLocalData:(NSObject *)localData;
 
 /**
  * isNewView - Used to track the first time the view is introduced into the hierarchy.  It is initialized YES, then is

React/Views/RCTShadowView.m

@@ -681,6 +681,13 @@ static inline YGSize RCTShadowViewMeasure(YGNodeRef node, float width, YGMeasure
   YGNodeMarkDirty(_yogaNode);
 }
 
+// Local Data
+
+- (void)setLocalData:(__unused NSObject *)localData
+{
+  // Do nothing by default.
+}
+
 // Flex
 
 - (void)setFlexBasis:(YGValue)value