Remove suppression for race condition in talk_base::Event.

tools/valgrind/tsan/suppressions.txt

 # There are a few kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 825 matching lines @@
 {
   bug_115540
   ThreadSanitizer:Race
   fun:base::Thread::message_loop
   fun:content::BrowserThreadImpl::PostTaskHelper
   fun:content::BrowserThread::PostTask
   fun:AudioRendererHost::OnCreated
   fun:media::AudioOutputController::DoCreate
 }
 {
-  bug_116421
-  ThreadSanitizer:Race
-  fun:talk_base::Event::EnsureInitialized
-}
-{
   bug_116559
   ThreadSanitizer:Race
   fun:logging::::LoggingTest_Dcheck_Test::TestBody
   fun:testing::internal::HandleSehExceptionsInMethodIfSupported
 }
 {
   bug_118319_a
   ThreadSanitizer:Race
   fun:content::BrowserThreadImpl::~BrowserThreadImpl
   fun:content::BrowserProcessSubThread::~BrowserProcessSubThread
@@ skipping 15 matching lines @@
   fun:content::BrowserThread::PostTask
   fun:PluginLoaderPosix::GetPluginsToLoad
   fun:base::internal::RunnableAdapter::Run
 }
 {
   bug_118319_c
   ThreadSanitizer:Race
   fun:base::Thread::ThreadMain
   fun:base::::ThreadFunc
 }