Removed undo flags from dialog field specs.

Since the undo flag is now automatically set to false in dialogs,
it's no longer necessary to specify it in the field specs.

Ticket #1394

install/ui/group.js

@@ -95,7 +95,6 @@ IPA.entity_factories.group =  function () {
                     factory: IPA.group_nonposix_checkbox_widget,
                     name: 'nonposix',
                     label: IPA.messages.objects.group.posix,
-                    undo: false,
                     checked: true
                 },
                 'gidnumber']