xmlrpcplus: use parent's int marshalling if possible

If we have an int value between xmlrpc.MININT and xmlrpc.MAXINT, we can
rely on stdlib's xmlrpc.Marshaller. This allows us to drop this custom
code.

koji/xmlrpcplus.py

@@ -47,9 +47,7 @@ class ExtendedMarshaller(xmlrpc_client.Marshaller):
             write(str(int(value)))
             write("</i8></value>\n")
         else:
-            write("<value><int>")
-            write(str(int(value)))
-            write("</int></value>\n")
+            return xmlrpc_client.Marshaller.dump_int(self, value, write)
     dispatch[int] = dump_int
 
     # we always want to allow None