Minor optimization in ignoreElements operator

We don't need to call any kind of `noop` function, simply do not call anything

src/operators/ignoreElements.ts

@@ -1,7 +1,6 @@
 import { Observable } from '../Observable';
 import { Operator } from '../Operator';
 import { Subscriber } from '../Subscriber';
-import { noop } from '../util/noop';
 import { MonoTypeOperatorFunction } from '../interfaces';
 
 /**
@@ -33,6 +32,6 @@ class IgnoreElementsOperator<T, R> implements Operator<T, R> {
  */
 class IgnoreElementsSubscriber<T> extends Subscriber<T> {
  protected _next(unused: T): void {
- noop();
+ // Do nothing
  }
 }