org-clock: Fix remnant UTC time in clock computation

* lisp/org-clock.el (org-clock-get-sum-start): Remove wrong UTC
  reference.

Reported-by: Jose Robins <jose.robins@gmail.com>
<http://lists.gnu.org/r/emacs-orgmode/2018-02/msg00018.html>

lisp/org-clock.el

@@ -1423,7 +1423,7 @@ The time is always returned as UTC."
       (current-time))
      ((equal cmt "today")
       (setq org--msg-extra "showing today's task time.")
-      (let* ((dt (org-decode-time nil t))
+      (let* ((dt (decode-time))
 	     (hour (nth 2 dt))
 	     (day (nth 3 dt)))
 	(if (< hour org-extend-today-until) (setf (nth 3 dt) (1- day)))