Avoid extra copy and use more expressive APIs

Summary: changelog: [internal]

Reviewed By: RSNara

Differential Revision: D30756211

fbshipit-source-id: 650b3faa55ce1b6f33a452f25b699d854a5cee25

ReactCommon/react/renderer/animations/LayoutAnimationKeyFrameManager.cpp

@@ -256,13 +256,12 @@ LayoutAnimationKeyFrameManager::pullTransaction(
       std::lock_guard<std::mutex> lock(currentAnimationMutex_);
       if (currentAnimation_) {
         currentAnimation = std::move(currentAnimation_);
-        currentAnimation_ = {};
+        currentAnimation_.reset();
       }
     }
 
-    if (currentAnimation) {
-      LayoutAnimation animation = std::move(currentAnimation.value());
-      currentAnimation = {};
+    if (currentAnimation.hasValue()) {
+      LayoutAnimation animation = std::move(currentAnimation).value();
       animation.surfaceId = surfaceId;
       animation.startTime = now;