Remove bugfix needed for webpack 4 when webpack 5 is used (#23886)

Tobias has fixed the `compiler.hooks.invalid.call()` bug in webpack 5 so this is no longer needed



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.

## Documentation / Examples

- [ ] Make sure the linting passes

.vscode/launch.json

@@ -12,6 +12,7 @@
       "runtimeExecutable": "yarn",
       "runtimeArgs": ["run", "debug", "dev", "test/integration/basic"],
       "skipFiles": ["<node_internals>/**"],
+      "outFiles": ["${workspaceFolder}/packages/next/dist/**/*"],
       "port": 9229
     },
     {

packages/next/server/on-demand-entry-handler.ts

@@ -2,7 +2,7 @@ import { EventEmitter } from 'events'
 import { IncomingMessage, ServerResponse } from 'http'
 import { join, posix } from 'path'
 import { parse } from 'url'
-import { webpack } from 'next/dist/compiled/webpack/webpack'
+import { webpack, isWebpack5 } from 'next/dist/compiled/webpack/webpack'
 import * as Log from '../build/output/log'
 import {
   normalizePagePath,
@@ -293,12 +293,14 @@ class Invalidator {
     }
 
     this.building = true
-    // Work around a bug in webpack, calling `invalidate` on Watching.js
-    // doesn't trigger the invalid call used to keep track of the `.done` hook on multiCompiler
-    for (const compiler of this.multiCompiler.compilers) {
-      // @ts-ignore TODO: Check if this is still needed with webpack 5
-      compiler.hooks.invalid.call()
+    if (!isWebpack5) {
+      // Work around a bug in webpack, calling `invalidate` on Watching.js
+      // doesn't trigger the invalid call used to keep track of the `.done` hook on multiCompiler
+      for (const compiler of this.multiCompiler.compilers) {
+        compiler.hooks.invalid.call()
+      }
     }
+
     this.watcher.invalidate()
   }