Remove old data for tests

scipost/fixtures/contributors.json

-[
-  {
-    "model": "auth.user",
-    "pk": 1,
-    "fields": {
-      "password": "pbkdf2_sha256$30000$iqtXX60Ahqcx$IKfNZNSMbSca/agzPXHTdEej3dXhQi1sK/MCrBTnuW4=",
-      "last_login": null,
-      "is_superuser": false,
-      "username": "Test",
-      "first_name": "Firstname",
-      "last_name": "Testuser",
-      "email": "testuser@test.com",
-      "is_staff": false,
-      "is_active": true,
-      "date_joined": "2016-12-14T20:41:31.282Z",
-      "groups": [
-        6
-      ],
-      "user_permissions": []
-    }
-  },
-  {
-    "model": "scipost.contributor",
-    "pk": 2,
-    "fields": {
-      "user": 1,
-      "status": 1,
-      "title": "MR",
-      "vetted_by": 2
-    }
-  }
-]

scipost/fixtures/groups.json

-[
-{
-    "model": "auth.group",
-    "pk": 1,
-    "fields": {
-        "name": "SciPost Administrators",
-        "permissions": [
-            143,
-            130,
-            131,
-            148,
-            128,
-            147,
-            139,
-            137,
-            140,
-            126,
-            138,
-            142
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 2,
-    "fields": {
-        "name": "Advisory Board",
-        "permissions": [
-            128
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 3,
-    "fields": {
-        "name": "Editorial Administrators",
-        "permissions": [
-            143,
-            148,
-            147,
-            149,
-            142
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 4,
-    "fields": {
-        "name": "Editorial College",
-        "permissions": [
-            144,
-            145,
-            142,
-            132
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 5,
-    "fields": {
-        "name": "Vetting Editors",
-        "permissions": [
-            139,
-            137,
-            140,
-            138
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 6,
-    "fields": {
-        "name": "Registered Contributors",
-        "permissions": [
-            134,
-            146,
-            135,
-            136,
-            133,
-            141
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 7,
-    "fields": {
-        "name": "Testers",
-        "permissions": []
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 8,
-    "fields": {
-        "name": "Ambassadors",
-        "permissions": [
-            128
-        ]
-    }
-},
-{
-    "model": "auth.group",
-    "pk": 9,
-    "fields": {
-        "name": "Junior Ambassadors",
-        "permissions": [
-            127
-        ]
-    }
-}
-]