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/common/test/forms-deprecated/directives_spec.ts

@@ -8,7 +8,7 @@
 
 import {afterEach, beforeEach, ddescribe, describe, expect, iit, inject, it, xit} from '@angular/core/testing/testing_internal';
 
-import {fakeAsync, flushMicrotasks, Log, tick,} from '@angular/core/testing';
+import {fakeAsync, flushMicrotasks, tick,} from '@angular/core/testing';
 
 import {SpyNgControl, SpyValueAccessor} from '../spies';
 

modules/@angular/common/test/forms-deprecated/model_spec.ts

@@ -7,7 +7,7 @@
  */
 
 import {ddescribe, describe, it, iit, xit, expect, beforeEach, afterEach, inject,} from '@angular/core/testing/testing_internal';
-import {fakeAsync, flushMicrotasks, Log, tick} from '@angular/core/testing';
+import {fakeAsync, flushMicrotasks, tick} from '@angular/core/testing';
 import {AsyncTestCompleter} from '@angular/core/testing/testing_internal';
 import {ControlGroup, Control, ControlArray, Validators} from '@angular/common/src/forms-deprecated';
 import {IS_DART, isPresent} from '../../src/facade/lang';

modules/@angular/common/test/forms-deprecated/validators_spec.ts

@@ -7,7 +7,7 @@
  */
 
 import {AbstractControl, Control, ControlArray, ControlGroup, Validators} from '@angular/common/src/forms-deprecated';
-import {Log, fakeAsync, flushMicrotasks, tick} from '@angular/core/testing';
+import {fakeAsync, flushMicrotasks, tick} from '@angular/core/testing';
 import {afterEach, beforeEach, ddescribe, describe, expect, iit, it, xit} from '@angular/core/testing/testing_internal';
 
 import {EventEmitter, ObservableWrapper, TimerWrapper} from '../../src/facade/async';