Bug 1331171 - Part 3: Remove xpcom checks for Windows Vista. r=froydnj

Also remove the #includes of some unused header files.

MozReview-Commit-ID: 6mRoIazEA3j

--HG--
extra : rebase_source : 6f96d22543509bf09b684b0bfbfa624eafc58b94

xpcom/build/XPCOMInit.cpp

@@ -111,7 +111,6 @@ extern nsresult nsStringInputStreamConstructor(nsISupports*, REFNSIID, void**);
 #include "SpecialSystemDirectory.h"
 
 #if defined(XP_WIN)
-#include "mozilla/WindowsVersion.h"
 #include "nsWindowsRegKey.h"
 #endif
 

xpcom/threads/nsThreadUtils.cpp

@@ -20,15 +20,10 @@
 
 #ifdef XP_WIN
 #include <windows.h>
-#include "mozilla/WindowsVersion.h"
-using mozilla::IsVistaOrLater;
 #elif defined(XP_MACOSX)
 #include <sys/resource.h>
 #endif
 
-#include <pratom.h>
-#include <prthread.h>
-
 using namespace mozilla;
 
 #ifndef XPCOM_GLUE_AVOID_NSPR
@@ -416,8 +411,7 @@ nsThreadPoolNaming::GetNextThreadName(const nsACString& aPoolName)
 nsAutoLowPriorityIO::nsAutoLowPriorityIO()
 {
 #if defined(XP_WIN)
-  lowIOPrioritySet = IsVistaOrLater() &&
-                     SetThreadPriority(GetCurrentThread(),
+  lowIOPrioritySet = SetThreadPriority(GetCurrentThread(),
                                        THREAD_MODE_BACKGROUND_BEGIN);
 #elif defined(XP_MACOSX)
   oldPriority = getiopolicy_np(IOPOL_TYPE_DISK, IOPOL_SCOPE_THREAD);