Remove Pupstagram references

Pupstagram is no longer an officially supported demo app, and the
code samples extracted from it work well enough by themselves in
the docs.

docs/source/performance/performance.mdx

@@ -85,7 +85,7 @@ cacheRedirects: {
 
 Prefetching is one of the easiest ways to make your application's UI feel a lot faster with Apollo Client. Prefetching simply means loading data into the cache before it needs to be rendered on the screen. Essentially, we want to load all data required for a view as soon as we can guess that a user will navigate to it.
 
-We can accomplish this in only a few lines of code by calling `client.query` whenever the user hovers over a link. Let's see this in action in the `Feed` component in our example app [Pupstagram](https://codesandbox.io/s/r5qp83z0yq).
+We can accomplish this in only a few lines of code by calling `client.query` whenever the user hovers over a link.
 
 <MultiCodeBlock>
 <div data-language="hooks-js">

docs/source/why-apollo.mdx

@@ -5,7 +5,7 @@ description: Why choose Apollo Client to manage your data?
 
 import { MultiCodeBlock } from 'gatsby-theme-apollo-docs';
 
-Data management shouldn't have to be so difficult! If you're wondering how to simplify managing remote and local data in your React application, then you've come to the right place. Through practical examples inspired by our [example app Pupstagram](https://codesandbox.io/s/r5qp83z0yq), you'll learn how Apollo's intelligent caching and declarative approach to data fetching can help you iterate faster while writing less code. Let's jump right in! 🚀
+Data management shouldn't have to be so difficult! If you're wondering how to simplify managing remote and local data in your React application, then you've come to the right place. Throughout this documentation, you'll learn how Apollo's intelligent caching and declarative approach to data fetching can help you iterate faster while writing less code. Let's jump right in! 🚀
 
 ## Declarative data fetching
 
@@ -51,7 +51,7 @@ You'll find that when you switch to Apollo Client, you'll be able to delete a lo
 
 ## Zero-config caching
 
-One of the key features that sets Apollo Client apart from other data management solutions is its normalized cache. Just by setting up Apollo Client, you get an intelligent cache out of the box with no additional configuration required. From the home page of the [Pupstagram example app](https://codesandbox.io/s/r5qp83z0yq), click one of the dogs to see its detail page. Then, go back to the home page. You'll notice that the images on the home page load instantaneously, thanks to the Apollo cache.
+One of the key features that sets Apollo Client apart from other data management solutions is its normalized cache. Just by setting up Apollo Client, you get an intelligent cache out of the box with no additional configuration required.
 
 ```js
 import { ApolloClient } from '@apollo/client';