Cleanup unmatched TRACE_EVENT_END in BrowserMainLoop::CreateThreads

Trace event left behind after matching TRACE_EVENT_BEGIN was removed in
https://chromium-review.googlesource.com/c/chromium/src/+/941264/26/content/browser/browser_main_loop.cc

R=jam@chromium.org

Bug: 815225
Change-Id: I5c1e2d94429e1b6366662ab01cda614a7246a4b3
Reviewed-on: https://chromium-review.googlesource.com/966933Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543835}

content/browser/browser_main_loop.cc

@@ -1009,7 +1009,6 @@ int BrowserMainLoop::CreateThreads() {
   DCHECK(io_thread_);
   io_thread_->InitIOThreadDelegate();
 
-  TRACE_EVENT_END0("startup", "BrowserMainLoop::CreateThreads:start");
   created_threads_ = true;
   return result_code_;
 }