Get rid of the non-standard ICOM_VFIELD macro.

diff --git a/dlls/dinput/dinput_main.c b/dlls/dinput/dinput_main.c
index c29e29d..50e47e1 100644
--- a/dlls/dinput/dinput_main.c
+++ b/dlls/dinput/dinput_main.c
@@ -627,7 +627,7 @@
 typedef struct
 {
     /* IUnknown fields */
-    ICOM_VFIELD(IClassFactory);
+    IClassFactoryVtbl          *lpVtbl;
     DWORD                       ref;
 } IClassFactoryImpl;