util: XML: Avoid forward function declaration

Recursive functions apparently don't need them, but I originally thought
they do.

src/util/virxml.c

@@ -932,11 +932,6 @@ virXMLNodeToString(xmlDocPtr doc,
 typedef int (*virXMLForeachCallback)(xmlNodePtr node,
                                      void *opaque);
 
-static int
-virXMLForeachNode(xmlNodePtr root,
-                  virXMLForeachCallback cb,
-                  void *opaque);
-
 static int
 virXMLForeachNode(xmlNodePtr root,
                   virXMLForeachCallback cb,