Correct SeAT API logic (#860)

* Do not attempt to change user email on SeAT if unchanged.
This prevents HTTP422 from being raised on password resets.

*Delete users on deactivation.
The existing disable user logic does nothing and results in a HTTP500.
It's safe to delete users entirely - the API keys are retained.

Fixes #844

services/modules/seat/tests.py

@@ -100,10 +100,10 @@ class SeatHooksTestCase(TestCase):
 
         # Test none user is deleted
         none_user = User.objects.get(username=self.none_user)
-        manager.disable_user.return_value = 'abc123'
+        manager.delete_user.return_value = 'abc123'
         SeatUser.objects.create(user=none_user, username='abc123')
         service.validate_user(none_user)
-        self.assertTrue(manager.disable_user.called)
+        self.assertTrue(manager.delete_user.called)
         with self.assertRaises(ObjectDoesNotExist):
             none_seat = User.objects.get(username=self.none_user).seat
 
@@ -115,7 +115,7 @@ class SeatHooksTestCase(TestCase):
         result = service.delete_user(member)
 
         self.assertTrue(result)
-        self.assertTrue(manager.disable_user.called)
+        self.assertTrue(manager.delete_user.called)
         with self.assertRaises(ObjectDoesNotExist):
             seat_user = User.objects.get(username=self.member).seat
 
@@ -177,7 +177,7 @@ class SeatViewsTestCase(TestCase):
 
         response = self.client.get(urls.reverse('auth_deactivate_seat'))
 
-        self.assertTrue(manager.disable_user.called)
+        self.assertTrue(manager.delete_user.called)
         self.assertRedirects(response, expected_url=urls.reverse('auth_services'), target_status_code=200)
         with self.assertRaises(ObjectDoesNotExist):
             seat_user = User.objects.get(pk=self.member.pk).seat