ref(api/fixtures): remove AnonymousUser

Newer versions of django-guardian ensure this object is already
created, which caused a collision in the unit tests.

Author: mboersma

rootfs/api/fixtures/test_sharing.json

@@ -1,22 +1,4 @@
 [
-{
-  "pk": -1,
-  "model": "auth.user",
-  "fields": {
-    "username": "AnonymousUser",
-    "first_name": "",
-    "last_name": "",
-    "is_active": true,
-    "is_superuser": false,
-    "is_staff": false,
-    "last_login": "2013-11-25T21:33:19.120Z",
-    "groups": [],
-    "user_permissions": [],
-    "password": "",
-    "email": "",
-    "date_joined": "2013-11-25T21:33:19.120Z"
-  }
-},
 {
   "pk": 2,
   "model": "auth.user",