include/winbase.h: Remove mistaken `#ifdef` around `THREAD_INFORMATION_CLASS`

Despite its introduction in Windows SDK v8.1, it is always available.

Signed-off-by: Liu Hao <lh_mouse@126.com>
diff --git a/mingw-w64-headers/include/winbase.h b/mingw-w64-headers/include/winbase.h
index 8dd03de..12d7875 100644
--- a/mingw-w64-headers/include/winbase.h
+++ b/mingw-w64-headers/include/winbase.h
@@ -1181,13 +1181,11 @@
   WINBASEAPI LPVOID WINAPI ConvertThreadToFiberEx (LPVOID lpParameter, DWORD dwFlags);
 #endif
 
-#if _WIN32_WINNT >= 0x0602
   typedef enum _THREAD_INFORMATION_CLASS {
     ThreadMemoryPriority,
     ThreadAbsoluteCpuPriority,
     ThreadInformationClassMax
   } THREAD_INFORMATION_CLASS;
-#endif
 
 #if WINAPI_FAMILY_PARTITION (WINAPI_PARTITION_DESKTOP)