org-clock: Use new entities for clock table

* lisp/org-clock.el (org-clocktable-indent-string): Use new entities.
  Update docstring.

Fixes: bug#18870

lisp/org-clock.el

@@ -2641,10 +2641,10 @@ from the dynamic block definition."
     total-time))
 
 (defun org-clocktable-indent-string (level)
+  "Return indentation string according to LEVEL.
+LEVEL is an integer.  Indent by two spaces per level above 1."
   (if (= level 1) ""
-    (let ((str " "))
-      (dotimes (k (1- level) str)
-	(setq str (concat "\\emsp" str))))))
+    (concat "\\" (make-string (- (* 2 level) 3) ?.) " ")))
 
 (defun org-clocktable-steps (params)
   "Step through the range to make a number of clock tables."