bring code to old state, make consistent with docs, Closes PR 13642 again

collects/2htdp/universe.rkt

@@ -327,7 +327,7 @@
          [hgt (image-height fst)])
     (big-bang 
      m* 
-     (on-tick rest (/ 1 r))
+     (on-tick rest r)
      (on-draw (lambda (m) (if (empty? m) (text "The End" 22 'red) (first m))))
      (stop-when empty?))))
 

collects/teachpack/2htdp/scribblings/universe.scrbl

@@ -127,8 +127,8 @@ Example:
 @defproc[(run-movie [r (and/c real? positive?)] [m [Listof image?]])
          true]{
 
- @racket[run-movie] displays the list of images @racket[m] at the rate of
- @racket[r] images per second.}
+ @racket[run-movie] displays the list of images @racket[m], spending 
+ @racket[r] seconds per image.}
 
 
 @;-----------------------------------------------------------------------------