Reduce the errors related to user fixtures

We were using user fixtures in a lot of parameterized tests, but this is
no longer allowed in Pytest 5. To avoid having to split up the parametrized
tests (which would make the test files a lot longer and slightly more
difficult to read) this commit creates functions which return various types
of user json so that we can use these as the test parameters instead.

tests/app/main/views/test_accept_invite.py

@@ -9,8 +9,8 @@ import app
 from tests.conftest import (
     SERVICE_ONE_ID,
     USER_ONE_ID,
-    active_caseworking_user,
-    active_user_with_permissions,
+    create_active_caseworking_user,
+    create_active_user_with_permissions,
     normalize_spaces,
 )
 
@@ -126,8 +126,8 @@ def test_invite_goes_in_session(
 
 
 @pytest.mark.parametrize('user, landing_page_title', [
-    (active_user_with_permissions, 'Dashboard'),
-    (active_caseworking_user, 'Templates'),
+    (create_active_user_with_permissions(), 'Dashboard'),
+    (create_active_caseworking_user(), 'Templates'),
 ])
 def test_accepting_invite_removes_invite_from_session(
     client_request,
@@ -153,7 +153,6 @@ def test_accepting_invite_removes_invite_from_session(
     user,
     landing_page_title,
 ):
-    user = user(fake_uuid)
     sample_invite['email_address'] = user['email_address']
 
     mocker.patch('app.invite_api_client.check_token', return_value=sample_invite)