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/core/test/debug/debug_node_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {NgFor, NgIf} from '@angular/common';
+
 import {Injectable, NO_ERRORS_SCHEMA} from '@angular/core';
 import {Component, Directive, Input} from '@angular/core/src/metadata';
 import {ComponentFixture, TestBed, async} from '@angular/core/testing';