libraries/winpthreads: remove unused dwFlags variable in sched.c

the usage of this variable was removed in 13c9e28c0e77fb9877e0580139e769b1de55f6c7 commit

Signed-off-by: Biswapriyo Nath <nathbappai@gmail.com>
Signed-off-by: Liu Hao <lh_mouse@126.com>
diff --git a/mingw-w64-libraries/winpthreads/src/sched.c b/mingw-w64-libraries/winpthreads/src/sched.c
index df3c60e..976bcc1 100644
--- a/mingw-w64-libraries/winpthreads/src/sched.c
+++ b/mingw-w64-libraries/winpthreads/src/sched.c
@@ -89,7 +89,7 @@
 static int pthread_check(pthread_t t)
 {
   struct _pthread_v *pv;
-  DWORD dwFlags;
+
   if (!t)
     return ESRCH;
   pv = __pth_gpointer_locked (t);