[MessageLoop] Remove logging of obsolete histogram unintentionally re-added

This was removed in r577553 but I unintentionally reintroduced it
in r578809 (incorrect rebase).

This regressed https://crbug.com/860801#c18

R=kylechar@chromium.org

Bug: 860801
Change-Id: Ia42d24f915d271832b59c481ebe77ee1bc6fd11d
Reviewed-on: https://chromium-review.googlesource.com/1175060Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583048}

base/message_loop/message_loop_task_runner.cc

@@ -146,9 +146,6 @@ bool MessageLoopTaskRunner::AddToIncomingQueue(const Location& from_here,
   }
 #endif
 
-  if (!delay.is_zero())
-    UMA_HISTOGRAM_LONG_TIMES("MessageLoop.DelayedTaskQueue.PostedDelay", delay);
-
   bool did_queue_task = false;
   bool was_empty;
   {