docs(core): move core examples into examples/core/ directory

This allows examples to be found during aio's `yarn serve-and-sync`, which only
looks for examples in `packages/examples/<packageName>/**/*`, where
`packageName` is the name of the package that the modified file belonged to;
e.g. `core`, `common`, etc.).

packages/examples/testing/ts/fake_async.ts

@@ -1,38 +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
- */
-
-import {discardPeriodicTasks, fakeAsync, tick} from '@angular/core/testing';
-
-
-// #docregion basic
-describe('this test', () => {
-  it('looks async but is synchronous', <any>fakeAsync((): void => {
-       let flag = false;
-       setTimeout(() => { flag = true; }, 100);
-       expect(flag).toBe(false);
-       tick(50);
-       expect(flag).toBe(false);
-       tick(50);
-       expect(flag).toBe(true);
-     }));
-});
-// #enddocregion
-
-// #docregion pending
-describe('this test', () => {
-  it('aborts a periodic timer', <any>fakeAsync((): void => {
-       // This timer is scheduled but doesn't need to complete for the
-       // test to pass (maybe it's a timeout for some operation).
-       // Leaving it will cause the test to fail...
-       setInterval(() => {}, 100);
-
-       // Unless we clean it up first.
-       discardPeriodicTasks();
-     }));
-});
-// #enddocregion