Remove unused property _rootTag RCTPropsAnimatedNode

Summary:
changelog: [internal]

`_rootTag` is never assigned to and never read, let's remove it.

Reviewed By: RSNara

Differential Revision: D30667860

fbshipit-source-id: f4b89ebe6b6d26559188b0e19682f5ac765d40b6

Libraries/NativeAnimation/Nodes/RCTPropsAnimatedNode.m

@@ -16,7 +16,6 @@
 @implementation RCTPropsAnimatedNode
 {
   NSNumber *_connectedViewTag;
-  NSNumber *_rootTag;
   NSString *_connectedViewName;
   __weak RCTBridge *_bridge;
   __weak id<RCTSurfacePresenterStub> _surfacePresenter;
@@ -48,7 +47,6 @@
   _connectedViewTag = viewTag;
   _connectedViewName = viewName;
   _managedByFabric = RCTUIManagerTypeForTagIsFabric(viewTag);
-  _rootTag = nil;
 }
 
 - (void)disconnectFromView:(NSNumber *)viewTag
@@ -58,7 +56,6 @@
   _connectedViewTag = nil;
   _connectedViewName = nil;
   _managedByFabric = NO;
-  _rootTag = nil;
 }
 
 - (void)updateView