Removes legacy TODOs in createfactory methods (#11942)

* Removes legacy TODO from createFactory()

* Removes legacy TODO from createFactoryWithValidation()

* Adds comment "Legacy hook: remove it"

This is based on Dan Abramov's suggestion (source:
https://github.com/facebook/react/pull/11942#issuecomment-354818632)

packages/react/src/ReactElement.js

@@ -266,7 +266,7 @@ export function createFactory(type) {
   // easily accessed on elements. E.g. `<Foo />.type === Foo`.
   // This should not be named `constructor` since this may not be the function
   // that created the element, and it may not even be a constructor.
-  // Legacy hook TODO: Warn if this is accessed
+  // Legacy hook: remove it
   factory.type = type;
   return factory;
 }

packages/react/src/ReactElementValidator.js

@@ -357,9 +357,8 @@ export function createElementWithValidation(type, props, children) {
 
 export function createFactoryWithValidation(type) {
   const validatedFactory = createElementWithValidation.bind(null, type);
-  // Legacy hook TODO: Warn if this is accessed
   validatedFactory.type = type;
-
+  // Legacy hook: remove it
   if (__DEV__) {
     Object.defineProperty(validatedFactory, 'type', {
       enumerable: false,