Deleting unnecessary Differentiator code

Summary:
In the new Flattening differ, I experimentally verified that these two code paths are not hit (or redundant) and deleted them.

One of the branches did nothing and the other produced duplicate DELETE mutations for the same tag, that is handled elsewhere.

Changelog: [Internal]

Reviewed By: fkgozali

Differential Revision: D23806161

fbshipit-source-id: 9ad2929e2d719a7b9b34640ed35f7a696103604b

ReactCommon/react/renderer/mounting/Differentiator.cpp

@@ -1076,11 +1076,7 @@ static void calculateShadowViewMutationsV2(
               for (auto &oldFlattenedNode : oldFlattenedNodes) {
                 auto unvisitedOldChildPairIt = unvisitedOldChildPairs.find(
                     oldFlattenedNode.shadowView.tag);
-                if (unvisitedOldChildPairIt != unvisitedOldChildPairs.end()) {
-                  // Node unvisited - delete it entirely
-                  deleteMutations.push_back(ShadowViewMutation::DeleteMutation(
-                      oldFlattenedNode.shadowView));
-                } else {
+                if (unvisitedOldChildPairIt == unvisitedOldChildPairs.end()) {
                   // Node was visited - make sure to remove it from
                   // "newRemainingPairs" map
                   auto newRemainingIt =
@@ -1202,11 +1198,7 @@ static void calculateShadowViewMutationsV2(
               for (auto &oldFlattenedNode : oldFlattenedNodes) {
                 auto unvisitedOldChildPairIt = unvisitedOldChildPairs.find(
                     oldFlattenedNode.shadowView.tag);
-                if (unvisitedOldChildPairIt != unvisitedOldChildPairs.end()) {
-                  // Node unvisited - delete it entirely
-                  deleteMutations.push_back(ShadowViewMutation::DeleteMutation(
-                      oldFlattenedNode.shadowView));
-                } else {
+                if (unvisitedOldChildPairIt == unvisitedOldChildPairs.end()) {
                   // Node was visited - make sure to remove it from
                   // "newRemainingPairs" map
                   auto newRemainingIt =