No emails, texts or letters for broadcast services

To make the interface as simple as possible we don’t want to mix up
sending other types of communication where services have the broadcast
permission.

This commit removes the other permissions once a service has been given
the broadcast permission by a platform admin user.

tests/app/main/views/service_settings/test_service_setting_permissions.py

@@ -1,4 +1,5 @@
 import functools
+from unittest.mock import call
 
 import pytest
 from flask import url_for
@@ -38,15 +39,34 @@ def test_service_set_permission_requires_platform_admin(
     )
 
 
-@pytest.mark.parametrize('permission, form_data, on', [
-    ('inbound_sms', 'True', True),
-    ('inbound_sms', 'False', False),
-    ('email_auth', 'True', True),
-    ('email_auth', 'False', False),
-    ('international_letters', 'True', True),
-    ('international_letters', 'False', False),
-    ('broadcast', 'True', True),
-    ('broadcast', 'False', False),
+@pytest.mark.parametrize('permission, form_data, expected_calls', [
+    ('inbound_sms', 'True', [
+        call('inbound_sms', on=True),
+    ]),
+    ('inbound_sms', 'False', [
+        call('inbound_sms', on=False),
+    ]),
+    ('email_auth', 'True', [
+        call('email_auth', on=True),
+    ]),
+    ('email_auth', 'False', [
+        call('email_auth', on=False),
+    ]),
+    ('international_letters', 'True', [
+        call('international_letters', on=True),
+    ]),
+    ('international_letters', 'False', [
+        call('international_letters', on=False),
+    ]),
+    ('broadcast', 'True', [
+        call('broadcast', on=True),
+        call('email', on=False),
+        call('sms', on=False),
+        call('letter', on=False),
+    ]),
+    ('broadcast', 'False', [
+        call('broadcast', on=False),
+    ]),
 ])
 def test_service_set_permission(
     mocker,
@@ -55,7 +75,7 @@ def test_service_set_permission(
     mock_get_inbound_number_for_service,
     permission,
     form_data,
-    on
+    expected_calls,
 ):
     force_permission = mocker.patch('app.models.service.Service.force_permission')
     response = platform_admin_client.post(
@@ -64,9 +84,7 @@ def test_service_set_permission(
     )
     assert response.status_code == 302
     assert response.location == url_for('main.service_settings', service_id=service_one['id'], _external=True)
-    force_permission.assert_called_with(
-        permission, on=on
-    )
+    assert force_permission.call_args_list == expected_calls
 
 
 @pytest.mark.parametrize('service_fields, endpoint, kwargs, text', [