chore(lint): remove unused imports (#11923)

This was done automatically by tslint, which can now fix issues it finds.
The fixer is still pending in PR https://github.com/palantir/tslint/pull/1568
Also I have a local bugfix for https://github.com/palantir/tslint/issues/1569
which causes too many imports to be deleted.

modules/@angular/forms/test/form_control_spec.ts

@@ -7,7 +7,7 @@
  */
 
 import {fakeAsync, tick} from '@angular/core/testing';
-import {AsyncTestCompleter, beforeEach, ddescribe, describe, iit, inject, it, xit} from '@angular/core/testing/testing_internal';
+import {AsyncTestCompleter, beforeEach, describe, inject, it} from '@angular/core/testing/testing_internal';
 import {FormControl, FormGroup, Validators} from '@angular/forms';
 
 import {EventEmitter} from '../src/facade/async';