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

runtime/bin/platform_win.cc

Index: runtime/bin/platform_win.cc
diff --git a/runtime/bin/platform_win.cc b/runtime/bin/platform_win.cc
index dc0554e80c732c692b7004642f7d5bd4fefe4df6..dd0812fd59005145a688b26e4544bf7d6d45d41c 100644
--- a/runtime/bin/platform_win.cc
+++ b/runtime/bin/platform_win.cc
@@ -14,10 +14,6 @@
 
 
 namespace dart {
-
-// Defined in vm/os_thread_win.cc
-extern bool private_flag_windows_run_tls_destructors;
-
 namespace bin {
 
 bool Platform::Initialize() {
@@ -110,7 +106,6 @@ char* Platform::ResolveExecutablePath() {
 }
 
 void Platform::Exit(int exit_code) {
-  ::dart::private_flag_windows_run_tls_destructors = false;
   // On Windows we use ExitProcess so that threads can't clobber the exit_code.
   // See: https://code.google.com/p/nativeclient/issues/detail?id=2870
   ::ExitProcess(exit_code);