remove reducer from server bundle (#40959)

This reducer takes a good chunk of the bundle but is never run on the server so we can eliminate it. 5-10ms wins from my manual benchmark runs.

![image](https://user-images.githubusercontent.com/11064311/192577550-4b2c3fa1-1ce9-456a-a635-d708e8200f2d.png)


## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## 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.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next/client/components/reducer.ts

@@ -615,7 +615,7 @@ type AppRouterState = {
 /**
  * Reducer that handles the app-router state updates.
  */
-export function reducer(
+function clientReducer(
   state: Readonly<AppRouterState>,
   action: Readonly<
     | ReloadAction
@@ -1108,3 +1108,20 @@ export function reducer(
       throw new Error('Unknown action')
   }
 }
+
+function serverReducer(
+  state: Readonly<AppRouterState>,
+  _action: Readonly<
+    | ReloadAction
+    | NavigateAction
+    | RestoreAction
+    | ServerPatchAction
+    | PrefetchAction
+  >
+): AppRouterState {
+  return state
+}
+
+// we don't run the client reducer on the server, so we use a noop function for better tree shaking
+export const reducer =
+  typeof window === 'undefined' ? serverReducer : clientReducer