Clean up landed experimental flags

packages/next/next-server/server/config.ts

@@ -52,8 +52,6 @@ const defaultConfig: { [key: string]: any } = {
     reactMode: 'legacy',
     workerThreads: false,
     basePath: '',
-    static404: true,
-    pages404: true,
   },
   future: {
     excludeDefaultMomentLocales: false,

packages/next/next-server/server/next-server.ts

@@ -114,7 +114,6 @@ export default class Server {
     documentMiddlewareEnabled: boolean
     hasCssMode: boolean
     dev?: boolean
-    pages404?: boolean
   }
   private compression?: Middleware
   private onErrorMiddleware?: ({ err }: { err: Error }) => Promise<void>
@@ -162,7 +161,6 @@ export default class Server {
       staticMarkup,
       buildId: this.buildId,
       generateEtags,
-      pages404: this.nextConfig.experimental.pages404,
     }
 
     // Only the `publicRuntimeConfig` key is exposed to the client side
@@ -866,7 +864,7 @@ export default class Server {
     opts: any
   ): Promise<string | null> {
     // we need to ensure the status code if /404 is visited directly
-    if (this.nextConfig.experimental.pages404 && pathname === '/404') {
+    if (pathname === '/404') {
       res.statusCode = 404
     }
 
@@ -1171,19 +1169,16 @@ export default class Server {
   ) {
     let result: null | FindComponentsResult = null
 
-    const { static404, pages404 } = this.nextConfig.experimental
     const is404 = res.statusCode === 404
     let using404Page = false
 
     // use static 404 page if available and is 404 response
     if (is404) {
-      if (static404) {
-        result = await this.findPageComponents('/_errors/404')
-      }
+      result = await this.findPageComponents('/_errors/404')
 
       // use 404 if /_errors/404 isn't available which occurs
       // during development and when _app has getInitialProps
-      if (!result && pages404) {
+      if (!result) {
         result = await this.findPageComponents('/404')
         using404Page = result !== null
       }

packages/next/next-server/server/render.tsx

@@ -145,7 +145,6 @@ type RenderOpts = LoadComponentsReturnType & {
   documentMiddlewareEnabled?: boolean
   isDataReq?: boolean
   params?: ParsedUrlQuery
-  pages404?: boolean
   previewProps: __ApiPreviewProps
 }
 
@@ -278,7 +277,6 @@ export async function renderToHTML(
     unstable_getServerProps,
     isDataReq,
     params,
-    pages404,
     previewProps,
   } = renderOpts
 
@@ -391,7 +389,7 @@ export async function renderToHTML(
       renderOpts.nextExport = true
     }
 
-    if (pages404 && pathname === '/404' && !isAutoExport) {
+    if (pathname === '/404' && !isAutoExport) {
       throw new Error(PAGES_404_GET_INITIAL_PROPS_ERROR)
     }
   }