Revert "Hack around TLS destructors firing after the process exits"

runtime/vm/os_thread_win.cc

Index: runtime/vm/os_thread_win.cc
diff --git a/runtime/vm/os_thread_win.cc b/runtime/vm/os_thread_win.cc
index fd8de38685fb401c88f85457d9994ed19673c1d9..81cd216c992c9fdbc80e146e0e5054d621e620cf 100644
--- a/runtime/vm/os_thread_win.cc
+++ b/runtime/vm/os_thread_win.cc
@@ -14,10 +14,6 @@
 
 namespace dart {
 
-// This flag is flipped by platform_win.cc when the process is exiting.
-// TODO(zra): Remove once VM shuts down cleanly.
-bool private_flag_windows_run_tls_destructors = true;
-
 class ThreadStartData {
  public:
   ThreadStartData(OSThread::ThreadStartFunction function, uword parameter)
@@ -638,9 +634,6 @@ void ThreadLocalData::Shutdown() {
 
 // Static callback function to call with each thread termination.
 void NTAPI OnDartThreadExit(PVOID module, DWORD reason, PVOID reserved) {
-  if (!dart::private_flag_windows_run_tls_destructors) {
-    return;
-  }
   // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+
   // and on W2K and W2K3. So don't assume it is sent.
   if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason) {