Remove duplicate devguide link from footer (#2834)

Author: hugovk

fixtures/sitetree_menus.json

@@ -607,30 +607,6 @@
         "access_permissions": []
     }
 },
-{
-    "model": "sitetree.treeitem",
-    "pk": 28,
-    "fields": {
-        "title": "Developer's Guide",
-        "hint": "",
-        "url": "https://devguide.python.org/",
-        "urlaspattern": false,
-        "tree": 1,
-        "hidden": false,
-        "alias": null,
-        "description": "",
-        "inmenu": true,
-        "inbreadcrumbs": true,
-        "insitetree": true,
-        "access_loggedin": false,
-        "access_guest": false,
-        "access_restricted": false,
-        "access_perm_type": 1,
-        "parent": 9,
-        "sort_order": 28,
-        "access_permissions": []
-    }
-},
 {
     "model": "sitetree.treeitem",
     "pk": 29,