client.gnt_node: Remove unnecessary lambda

Pylint complained that the “lambda may not be necessary”. Turns out it
was right.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>

lib/client/gnt_node.py

@@ -211,7 +211,7 @@ def ListNodes(opts, args):
   selected_fields = ParseFields(opts.output, _LIST_DEF_FIELDS)
 
   fmtoverride = dict.fromkeys(["pinst_list", "sinst_list", "tags"],
-                              (lambda value: ",".join(value), False))
+                              (",".join, False))
 
   return GenericList(constants.QR_NODE, selected_fields, args, opts.units,
                      opts.separator, not opts.no_headers,