Test to be automated MDLQA-2502.

In this case, there's coverage for marking guides removal in grade/grading/form/guide/tests/behat/delete_marking_guide.feature, the goal here is to check what's missing and add to the test.

Testing instructions

 Test Pre-requisites:

• an existing assignment set to use a marking guide with a complete guide defined, and marking complete
• unless otherwise specified testing should be performed as a teacher user

Test Steps:

1. Edit the assignment, changing the grading method to Simple grading
2. Check that the grade (and feedback comment if used) for the marking already completed remains the same
3. Login as a student whose submission has been marked
4. Check that they can see the grade
5. Login as the teacher
6. Edit the assignment, changing the grading method to Marking guide
7. Check that the Marking guide details and information remains as it was before changing to Simple grading
8. Login as a student whose submission has been marked
9. Check that they can see the grade
10. Login as the teacher
11. Delete the marking guide from the assignment
12. Check that a warning is displayed, saying the detailed marking as per marking guide will be lost.
13. Cancel the deletion
14. Check that nothing has been lost
15. Delete the marking guide from the assignment and confirm the deletion
16. Check that the grade (and feedback comment if used) for the marking already completed remains the same
17. Check that marking can now be completed using the Simple grading interface