refactor(Observable): remove unnecessary if (#6505)

there is an unnecessary if in the pipe, remove it

#6504

src/internal/Observable.ts

@@ -436,7 +436,7 @@ export class Observable<T> implements Subscribable<T> {
  * ```
  */
  pipe(...operations: OperatorFunction<any, any>[]): Observable<any> {
- return operations.length ? pipeFromArray(operations)(this) : this;
+ return pipeFromArray(operations)(this);
  }
 
  /* tslint:disable:max-line-length */