Remove deprecated webpack5 config option (#41667)

This option doesn't do anything except print an error since Next.js 12,
so we can remove it. See previous upgrade guide:


https://github.com/vercel/next.js/blob/canary/docs/upgrading.md#upgrade-nextjs-version-to-12

packages/next/server/config-schema.ts

@@ -439,11 +439,6 @@ const configSchema = {
       isFunction: true,
       errorMessage: 'must be a function that returns a Promise',
     } as any,
-    future: {
-      additionalProperties: false,
-      properties: {},
-      type: 'object',
-    },
     generateBuildId: {
       isFunction: true,
       errorMessage: 'must be a function that returns a Promise',

packages/next/server/config-shared.ts

@@ -233,12 +233,6 @@ export interface NextConfig extends Record<string, any> {
    */
   redirects?: () => Promise<Redirect[]>
 
-  /**
-   * @deprecated This option has been removed as webpack 5 is now default
-   * @see [Next.js webpack 5 documentation](https://nextjs.org/docs/messages/webpack5) for upgrading guidance.
-   */
-  webpack5?: false
-
   /**
    * @see [Moment.js locales excluded by default](https://nextjs.org/docs/upgrading#momentjs-locales-excluded-by-default)
    */
@@ -405,13 +399,6 @@ export interface NextConfig extends Record<string, any> {
    */
   httpAgentOptions?: { keepAlive?: boolean }
 
-  future?: {
-    /**
-     * @deprecated This option has been removed as webpack 5 is now default
-     */
-    webpack5?: false
-  }
-
   /**
    * During a build, Next.js will automatically trace each page and its dependencies to determine all of the files
    * that are needed for deploying a production version of your application.
@@ -539,7 +526,6 @@ export const defaultConfig: NextConfig = {
   i18n: null,
   productionBrowserSourceMaps: false,
   optimizeFonts: true,
-  webpack5: undefined,
   excludeDefaultMomentLocales: true,
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},

packages/next/server/config.ts

@@ -520,12 +520,6 @@ function assignDefaults(dir: string, userConfig: { [key: string]: any }) {
     }
   }
 
-  if (result.webpack5 === false) {
-    throw new Error(
-      `Webpack 4 is no longer supported in Next.js. Please upgrade to webpack 5 by removing "webpack5: false" from ${configFileName}. https://nextjs.org/docs/messages/webpack5`
-    )
-  }
-
   if (result.experimental && 'relay' in (result.experimental as any)) {
     Log.warn(
       `\`relay\` has been moved out of \`experimental\` and into \`compiler\`. Please update your ${configFileName} file accordingly.`