Remove experimental Heisentest hack code

Author: greghendershott

racket/scribble.rkt

@@ -254,15 +254,6 @@
                              what)])))))
 
 (module+ test
-  ;; Experimental hack to debug test failures happening only on CI and
-  ;; only for Racket 6.12 (not stable or snapshot versions), where
-  ;; xref-index seems to return an empty list.
-  (when (getenv "CI")
-    (let loop ()
-      (when (null? (xref-index (load-collections-xref)))
-        (displayln "Waiting 5 seconds for xref-index...")
-        (sleep 5)
-        (loop))))
   (define older?
     (not (safe-dynamic-require 'scribble/manual-struct 'index-desc?)))
   (define (check-lookup term kind libs fams)