Delete rerun submission deletes original submission

[ihsaan-ullah]

@ mention of reviewers

@Didayolo

A brief description of the purpose of the changes contained in this PR.

We had two problems:

1. When you delete a rerun submission, its original submission is also deleted
2. When you delete original submission, its rerun submissions are also deleted.

NOW this PR fixes this problem i.e. do not delete original submission when a reun is deleted, similarly do not delete rerun submissions when original is deleted

Issues this PR resolves

• Delete submission problem #1300
• Problems with re-running submissions #1182 -> Deleting a re-run submission also delete the original submission
• deleting rerun submission also deletes previous submission #1178

A checklist for hand testing

• upload a submission
• rerun this submission (it will create a new submission)
• delete the rerun submission and check that the original submission is NOT deleted
• rerun the original submission again multiple times
• delete the original submission and check that the rerun submission are NOT deleted

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge