Remove custom error message from personalisation validation

There's no longer a single err msg that fits all problems with
personalisation - since letters expect specific fields there

tests/app/v2/notifications/test_notification_schemas.py

@@ -127,7 +127,7 @@ def test_post_sms_schema_with_personalisation_that_is_not_a_dict():
     error = json.loads(str(e.value))
     assert len(error.get('errors')) == 1
     assert error['errors'] == [{'error': 'ValidationError',
-                                'message': "personalisation should contain key value pairs"}]
+                                'message': "personalisation not_a_dict is not of type object"}]
     assert error.get('status_code') == 400
     assert len(error.keys()) == 2
 

tests/app/v2/notifications/test_post_letter_notifications.py

@@ -100,6 +100,26 @@ def test_notification_returns_400_for_schema_problems(
     }]
 
 
+def test_notification_returns_400_if_address_doesnt_have_underscores(
+    client,
+    sample_letter_template
+):
+    data = {
+        'template_id': str(sample_letter_template.id),
+        'personalisation': {
+            'address line 1': 'Her Royal Highness Queen Elizabeth II',
+            'postcode': 'SW1 1AA',
+        }
+    }
+
+    error_json = letter_request(client, data, service_id=sample_letter_template.service_id, _expected_status=400)
+
+    assert error_json['status_code'] == 400
+    assert error_json['errors'] == [{
+        'error': 'ValidationError',
+        'message': 'personalisation address_line_1 is a required property'
+    }]
+
 
 def test_returns_a_429_limit_exceeded_if_rate_limit_exceeded(
     client,