message: refactor(common): code cleaning
  * removing guard as console.warn is now widely supported
  * Couldn't remove non-null assertion, waiting for TS support of getters with different types (microsoft/typescript#43662)
  PR Close
diff: @@ -168,13 +168,10 @@ export class NgForOf<T, U extends NgIterable<T> = NgIterable<T>> implements DoCh
  @Input()
  set ngForTrackBy(fn: TrackByFunction<T>) {
  if (NG_DEV_MODE && fn != null && typeof fn !== 'function') {
  - // TODO(vicb): use a log service once there is a public one available
  - if (<any>console && <any>console.warn) {
  console.warn(
  `trackBy must be a function, but received ${JSON.stringify(fn)}. ` +
  `See https://angular.io/api/common/NgForOf#change-propagation for more information.`);
  }
  - }
  this._trackByFn = fn;
  }
  @@ -185,7 +182,9 @@ export class NgForOf<T, U extends NgIterable<T> = NgIterable<T>> implements DoCh
  private _ngForOf: U|undefined|null = null;
  private _ngForOfDirty: boolean = true;
  private _differ: IterableDiffer<T>|null = null;
  - // TODO(issue/24571): remove '!'.
  + // TODO(issue/24571): remove '!'
  + // waiting for microsoft/typescript#43662 to allow the return type `TrackByFunction|undefined` for
  + // the getter
  private _trackByFn!: TrackByFunction<T>;
  constructor(
  