relaxng: Remove useless if statement

ctxt and define are non-NULL at this point.

Fixes #482.
diff --git a/relaxng.c b/relaxng.c
index a72c715..acf536a 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -7987,12 +7987,7 @@
             ctxt->errNo = XML_RELAXNG_ERR_INTERNAL;
         return;
     }
-    if ((ctxt == NULL) || (define == NULL)) {
-        fprintf(stderr, "callback on %s missing info\n", token);
-        if ((ctxt != NULL) && (ctxt->errNo == XML_RELAXNG_OK))
-            ctxt->errNo = XML_RELAXNG_ERR_INTERNAL;
-        return;
-    } else if (define->type != XML_RELAXNG_ELEMENT) {
+    if (define->type != XML_RELAXNG_ELEMENT) {
         fprintf(stderr, "callback on %s define is not element\n", token);
         if (ctxt->errNo == XML_RELAXNG_OK)
             ctxt->errNo = XML_RELAXNG_ERR_INTERNAL;