fix(core/testing): clean up the core testing public API (#9466)

Previously, we were exporting internal mocks and helpers. Move these
to core/testing/testing_internal or remove them if they were
never used.

Remove deprecated items - injectAsync, clearPendingTimers.

BREAKING CHANGE:

Remove the following APIs from `@angular/core/testing`, which have been deprecated or were
never intended to be publicly exported:

```
injectAsync
clearPendingTimers
Log
MockAppliacationHref
MockNgZone
clearPendingTimers
getTypeOf
instantiateType
```

Instead of `injectAsync`, use `async(inject())`.

`clearPendingTimers` is no longer required.

modules/@angular/core/testing/testing_internal.ts

@@ -18,6 +18,9 @@ export {MockAnimationPlayer} from './animation/mock_animation_player';
 export {AsyncTestCompleter} from './async_test_completer';
 export {inject} from './test_injector';
 export {expect} from './testing';
+export * from './logger';
+export * from './ng_zone_mock';
+export * from './mock_application_ref';
 
 export var proxy: ClassDecorator = (t: any /** TODO #9100 */) => t;