refactor(router): remove history property

BREAKING CHANGE: the history property was marked as internal already. Since we
need to pass the history instance to the router, we always have access to it,
differently from Vue Router 3 where the history was instantiated internally.
The history API was also internal (it wasn't documented), so this change
shouldn't be a problem as people shouldn't be relying on `router.history` in
their apps. If you think this property is needed, please open an issue to
discuss the use case. Note it's already accessible as you have to create it:
```js
export const history = createWebHistory()
export const router = createRouter({ history, routes: [] })
```

src/router.ts

@@ -144,7 +144,7 @@ export interface Router {
   /**
    * @internal
    */
-  readonly history: RouterHistory
+  // readonly history: RouterHistory
   readonly currentRoute: Ref<RouteLocationNormalizedLoaded>
   readonly options: RouterOptions
 
@@ -910,7 +910,6 @@ export function createRouter(options: RouterOptions): Router {
     onError: errorHandlers.add,
     isReady,
 
-    history: routerHistory,
     install(app: App) {
       const router = this
       app.component('RouterLink', RouterLink)