fix(platform-browser/testing): clean up public api for platform-browser/testing (#9519)

Mostly, removing things that were never intended to be exported publicy.

BREAKING CHANGE:

The following are no longer publicly exported APIs. They were intended as internal
utilities and you should use your own util:

```
browserDetection,
dispatchEvent,
el,
normalizeCSS,
stringifyElement,
expect (and custom matchers for Jasmine)
```

modules/@angular/platform-browser-dynamic/test/xhr/xhr_cache_spec.ts

@@ -10,10 +10,10 @@ import {UrlResolver, XHR} from '@angular/compiler';
 import {Component, provide} from '@angular/core';
 import {beforeEach, beforeEachProviders, ddescribe, describe, iit, inject, it, xit} from '@angular/core/testing/testing_internal';
 import {AsyncTestCompleter} from '@angular/core/testing/testing_internal';
-import {expect} from '@angular/platform-browser/testing';
 
 import {fakeAsync, flushMicrotasks, Log, tick,} from '@angular/core/testing';
 import {TestComponentBuilder, ComponentFixture} from '@angular/compiler/testing';
+import {expect} from '@angular/platform-browser/testing/matchers';
 import {BaseException} from '../../src/facade/exceptions';
 import {CachedXHR} from '../../src/xhr/xhr_cache';
 import {setTemplateCache} from './xhr_cache_setter';

modules/@angular/platform-browser-dynamic/testing/dom_test_component_renderer.ts

@@ -9,7 +9,6 @@
 import {TestComponentRenderer} from '@angular/compiler/testing';
 import {Inject, Injectable} from '@angular/core';
 import {DOCUMENT} from '@angular/platform-browser';
-import {el} from '@angular/platform-browser/testing';
 
 import {getDOM} from '../platform_browser_private';
 
@@ -23,7 +22,8 @@ export class DOMTestComponentRenderer extends TestComponentRenderer {
   constructor(@Inject(DOCUMENT) private _doc: any /** TODO #9100 */) { super(); }
 
   insertRootElement(rootElId: string) {
-    let rootEl = el(`<div id="${rootElId}"></div>`);
+    let rootEl = <HTMLElement>getDOM().firstChild(
+        getDOM().content(getDOM().createTemplate(`<div id="${rootElId}"></div>`)));
 
     // TODO(juliemr): can/should this be optional?
     let oldRoots = getDOM().querySelectorAll(this._doc, '[id^=root]');