docs: remove previews (#2372)

Author: wolfy1339

README.md

@@ -17,12 +17,12 @@ The `octokit` package integrates the three main Octokit libraries
 - [`Octokit` API Client](#octokit-api-client)
   - [Constructor options](#constructor-options)
   - [Authentication](#authentication)
-  - [Proxy Servers](#proxy-servers-nodejs-only)
+  - [Proxy Servers (Node.js only)](#proxy-servers-nodejs-only)
   - [REST API](#rest-api)
     - [`octokit.rest` endpoint methods](#octokitrest-endpoint-methods)
     - [`octokit.request()`](#octokitrequest)
     - [Pagination](#pagination)
-    - [Media Type previews and formats](#media-type-previews-and-formats)
+    - [Media Type formats](#media-type-formats)
   - [GraphQL API queries](#graphql-api-queries)
     - [Schema previews](#schema-previews)
 - [App client](#app-client)
@@ -514,11 +514,9 @@ const issues = await octokit.paginate(octokit.rest.issues.listForRepo, {
 });
 ```
 
-#### Media Type previews and formats
+#### Media Type formats
 
-**Note**: The concept of _preview headers_ has been deprecated from REST API endpoints hosted via `api.github.com` but it still exists in GHES (GitHub Enterprise Server) version 3.2 and below. Instead of using _preview headers_ going forward, new features are now being tested using beta previews that users will have to opt-in to.
-
-Media type previews and formats can be set using `mediaType: { format, previews }` on every request. Required API previews are set automatically on the respective REST API endpoint methods.
+Media type formats can be set using `mediaType: { format }` on every request.
 
 Example: retrieve the raw content of a `package.json` file
 
@@ -534,20 +532,7 @@ const { data } = await octokit.rest.repos.getContent({
 console.log("package name: %s", JSON.parse(data).name);
 ```
 
-Example: retrieve a repository with topics
-
-```js
-const { data } = await octokit.rest.repos.getContent({
-  mediaType: {
-    previews: ["mercy"],
-  },
-  owner: "octocat",
-  repo: "hello-world",
-});
-console.log("topics on octocat/hello-world: %j", data.topics);
-```
-
-Learn more about [Media type formats](https://docs.github.com/en/rest/overview/media-types) and [previews](https://docs.github.com/en/[email protected]/rest/overview/api-previews) used on GitHub Enterprise Server.
+Learn more about [Media type formats](https://docs.github.com/en/rest/overview/media-types).
 
 ### GraphQL API queries