; Revert "; Add a note about a bottleneck"

This reverts commit 9f9ce631a2.

It's still a bottleneck, but so are mapcar (with its effect on GC) and
concat. So our limits show in several places at once.

lisp/progmodes/project.el

@@ -396,8 +396,6 @@ backend implementation of `project-external-roots'.")
        (setq files
              (mapcar
               (lambda (file) (concat default-directory file))
-              ;; XXX: With large enough project, split-string becomes
-              ;; one of the bottlenecks.
               (split-string
                (apply #'vc-git--run-command-string nil "ls-files" args)
                "\0" t)))