docs(reactive-forms): fix repeated file names (#3286)

* Fix typo (repeated file names)

* Correct subparagraph

Correct subparagraph in accordance with @kapunahelewong suggestion.
Add separate info about imports from `rxjs` lib for `hero-list.component.ts` and `hero.service.ts`.

Author: AlexanderLukin

public/docs/ts/latest/guide/reactive-forms.jade

@@ -775,8 +775,8 @@ figure.image-display
   If you're coding along with the steps in this reactive forms tutorial, 
   create the pertinent files based on the 
   [source code displayed below](#source-code "Reactive Forms source code"). 
-  Notice that `hero-list.component.ts` and `hero-list.component.ts` 
-  import `Observable` and `finally` from `rxjs`. 
+  Notice that `hero-list.component.ts` imports `Observable` and `finally` while `hero.service.ts` imports `Observable`, `of`,
+  and `delay` from `rxjs`. 
   Then return here to learn about _form array_ properties.
 
 .l-main-section