refactor(router): update test based on router quick-cancelling ongoing navigations (#25740)

PR Close #25740

packages/router/src/utils/assert.ts

@@ -1,19 +0,0 @@
-/**
- * @license
- * Copyright Google Inc. All Rights Reserved.
- *
- * Use of this source code is governed by an MIT-style license that can be
- * found in the LICENSE file at https://angular.io/license
- */
-
-export function assertDefined<T>(actual: T, msg: string) {
-  if (actual == null) {
-    throwError(msg);
-  }
-}
-
-function throwError(msg: string): never {
-  // tslint:disable-next-line
-  debugger;  // Left intentionally for better debugger experience.
-  throw new Error(`ASSERTION ERROR: ${msg}`);
-}