Remove now-unused prepareToManageChildren

This was a temporary hook needed for the DOM implementation. We no longer need it because we now necessarily load every node into cache (via calling getNativeNode on it) before manipulating any of its siblings.

src/renderers/dom/shared/ReactDOMComponent.js

@@ -1080,16 +1080,7 @@ ReactPerf.measureMethods(ReactDOMComponent.Mixin, 'ReactDOMComponent', {
 assign(
   ReactDOMComponent.prototype,
   ReactDOMComponent.Mixin,
-  ReactMultiChild.Mixin,
-  {
-    prepareToManageChildren: function() {
-      // Before we add, remove, or reorder the children of a node, make sure
-      // we have references to all of its children so we don't lose them, even
-      // if nefarious browser plugins add extra nodes to our tree. This could be
-      // called once per child so it should be fast.
-      ReactDOMComponentTree.precacheChildNodes(this, getNode(this));
-    },
-  }
+  ReactMultiChild.Mixin
 );
 
 module.exports = ReactDOMComponent;

src/renderers/shared/reconciler/ReactMultiChild.js

@@ -354,7 +354,6 @@ var ReactMultiChild = {
         }
       }
       if (updates) {
-        this.prepareToManageChildren();
         processQueue(this, updates);
       }
       this._renderedChildren = nextChildren;
@@ -373,14 +372,6 @@ var ReactMultiChild = {
       this._renderedChildren = null;
     },
 
-    /**
-     * Hook used by the DOM implementation to precache the nodes before we apply
-     * any reorders here.
-     */
-    prepareToManageChildren: function() {
-      // TODO: This sucks. Figure out a better design here.
-    },
-
     /**
      * Moves a child component to the supplied index.
      *