Remove unnecessary WNDPROC casts.

diff --git a/dlls/comctl32/header.c b/dlls/comctl32/header.c
index cb4ec0b..743725c 100644
--- a/dlls/comctl32/header.c
+++ b/dlls/comctl32/header.c
@@ -1842,7 +1842,7 @@
 
     ZeroMemory (&wndClass, sizeof(WNDCLASSA));
     wndClass.style         = CS_GLOBALCLASS | CS_DBLCLKS;
-    wndClass.lpfnWndProc   = (WNDPROC)HEADER_WindowProc;
+    wndClass.lpfnWndProc   = HEADER_WindowProc;
     wndClass.cbClsExtra    = 0;
     wndClass.cbWndExtra    = sizeof(HEADER_INFO *);
     wndClass.hCursor       = LoadCursorA (0, (LPSTR)IDC_ARROW);