Remove gs_critsectThreadDelete which was never used

This variable was added back in 3ef22a5b02 (trying to fix race
conditions. double deletions and memory leaks on thread termination...,
2003-09-21), but not used even then, nor ever since, so just remove it.

src/msw/thread.cpp

@@ -109,11 +109,6 @@ static wxCriticalSection *gs_critsectGui = NULL;
 // critical section which protects gs_nWaitingForGui variable
 static wxCriticalSection *gs_critsectWaitingForGui = NULL;
 
-// critical section which serializes WinThreadStart() and WaitForTerminate()
-// (this is a potential bottleneck, we use a single crit sect for all threads
-// in the system, but normally time spent inside it should be quite short)
-static wxCriticalSection *gs_critsectThreadDelete = NULL;
-
 // number of threads waiting for GUI in wxMutexGuiEnter()
 static size_t gs_nWaitingForGui = 0;
 
@@ -1259,8 +1254,6 @@ bool wxThreadModule::OnInit()
     gs_critsectGui = new wxCriticalSection();
     gs_critsectGui->Enter();
 
-    gs_critsectThreadDelete = new wxCriticalSection;
-
     wxThread::ms_idMainThread = wxThread::GetCurrentId();
 
     return true;
@@ -1277,8 +1270,6 @@ void wxThreadModule::OnExit()
     // library is initialized again later
     gs_tlsThisThread = TLS_OUT_OF_INDEXES;
 
-    wxDELETE(gs_critsectThreadDelete);
-
     if ( gs_critsectGui )
     {
         gs_critsectGui->Leave();