Fabric: Simplified `RootShadowNode` instantiation

Summary:
@public
Trivial.
`children = ShadowNode::emptySharedShadowNodeSharedList()` is already a default.

Reviewed By: rsnara

Differential Revision: D9650218

fbshipit-source-id: ad5c17776866b1dc800f68b0a54b9ac3f70de3f6

ReactCommon/fabric/uimanager/ShadowTree.cpp

@@ -25,7 +25,6 @@ ShadowTree::ShadowTree(Tag rootTag):
       .rootTag = rootTag,
       .props = RootShadowNode::defaultSharedProps(),
       .eventEmitter = noopEventEmitter,
-      .children = ShadowNode::emptySharedShadowNodeSharedList(),
     },
     nullptr
   );