message: refactor(schedulePromise): remove unnecessary subscription
diff: +/** @prettier */
  import { Observable } from '../Observable';
  import { SchedulerLike } from '../types';
  -import { Subscription } from '../Subscription';
  export function schedulePromise<T>(input: PromiseLike<T>, scheduler: SchedulerLike) {
  - return new Observable<T>(subscriber => {
  - const sub = new Subscription();
  - sub.add(scheduler.schedule(() => input.then(
  - value => {
  - sub.add(scheduler.schedule(() => {
  + return new Observable<T>((subscriber) => {
  + return scheduler.schedule(() =>
  + input.then(
  + (value) => {
  + subscriber.add(
  + scheduler.schedule(() => {
  subscriber.next(value);
  - sub.add(scheduler.schedule(() => subscriber.complete()));
  - }));
  + subscriber.add(scheduler.schedule(() => subscriber.complete()));
  + })
  + );
  },
  - err => {
  - sub.add(scheduler.schedule(() => subscriber.error(err)));
  + (err) => {
  + subscriber.add(scheduler.schedule(() => subscriber.error(err)));
  }
  - )));
  - return sub;
  + )
  + );
  });
  }
  