vo_null: don't reject hwaccel formats

This is not strictly needed anymore. (On the other hand, it's not really
possible to do hw decoding with vo_null, because the VO is still
responsible for opening the hw decoder API, but that's another story.)

video/out/vo_null.c

@@ -40,8 +40,6 @@ static void flip_page(struct vo *vo)
 
 static int query_format(struct vo *vo, uint32_t format)
 {
-    if (IMGFMT_IS_HWACCEL(format))
-        return 0;
     return VFCAP_CSP_SUPPORTED;
 }