Stop Unnecessary Purging of Node Cache

When each component unmounts, it already cleans up its respective entry in the node cache. Let's stop blowing away the entire node cache unnecessarily.

This should improve performance because a React component's root will never need to be searched for more than once.

src/core/ReactDOMIDOperations.js

@@ -161,7 +161,6 @@ var ReactDOMIDOperations = {
   dangerouslyReplaceNodeWithMarkupByID: function(id, markup) {
     var node = ReactID.getNode(id);
     DOMChildrenOperations.dangerouslyReplaceNodeWithMarkup(node, markup);
-    ReactID.purgeEntireCache();
   },
 
   /**
@@ -171,7 +170,6 @@ var ReactDOMIDOperations = {
   manageChildrenByParentID: function(parentID, domOperations) {
     var parent = ReactID.getNode(parentID);
     DOMChildrenOperations.manageChildren(parent, domOperations);
-    ReactID.purgeEntireCache();
   }
 
 };

src/core/ReactID.js

@@ -158,16 +158,8 @@ function purgeID(id) {
   delete nodeCache[id];
 }
 
-/**
- * Clears the entire cache.
- */
-function purgeEntireCache() {
-  nodeCache = {};
-}
-
 exports.ATTR_NAME = ATTR_NAME;
 exports.getID = getID;
 exports.setID = setID;
 exports.getNode = getNode;
 exports.purgeID = purgeID;
-exports.purgeEntireCache = purgeEntireCache;