core: add general admin.py loader, remove individual files

passbook/lib/admin.py

@@ -1,22 +0,0 @@
-"""passbook core admin"""
-
-from django.apps import apps
-from django.contrib import admin
-from django.contrib.admin.sites import AlreadyRegistered
-from django.contrib.auth.admin import UserAdmin
-from guardian.admin import GuardedModelAdmin
-
-from passbook.core.models import User
-
-
-def admin_autoregister(app):
-    """Automatically register all models from app"""
-    app_models = apps.get_app_config(app).get_models()
-    for model in app_models:
-        try:
-            admin.site.register(model, GuardedModelAdmin)
-        except AlreadyRegistered:
-            pass
-
-
-admin.site.register(User, UserAdmin)