Clean up Redux example (#4594)

- Remove unused imports

- Edit some comments

- Rename Wrapper App Class

examples/with-redux/lib/with-redux-store.js

-import App, {Container} from 'next/app'
-import {Provider} from 'react-redux'
+import React from 'react'
 import {initializeStore} from '../store'
 
 const isServer = typeof window === 'undefined'
@@ -11,7 +10,7 @@ function getOrCreateStore(initialState) {
     return initializeStore(initialState)
   }
 
-  // Store in global variable if client
+  // Create store if unavailable on the client and set it on the window object
   if (!window[__NEXT_REDUX_STORE__]) {
     window[__NEXT_REDUX_STORE__] = initializeStore(initialState)
   }
@@ -19,16 +18,18 @@ function getOrCreateStore(initialState) {
 }
 
 export default (App) => {
-  return class Redux extends React.Component {
+  return class AppWithRedux extends React.Component {
     static async getInitialProps (appContext) {
+      // Get or Create the store with `undefined` as initialState
+      // This allows you to set a custom default initialState
       const reduxStore = getOrCreateStore()
 
       // Provide the store to getInitialProps of pages
       appContext.ctx.reduxStore = reduxStore
 
       let appProps = {}
-      if (App.getInitialProps) {
-        appProps = await App.getInitialProps(appContext)
+      if (typeof App.getInitialProps === 'function') {
+        appProps = await App.getInitialProps.call(App, appContext)
       }
 
       return {