AO3-5743 Related works count in dashboard sidebar didn't decrease and sections didn't disappear when a parent work was deleted

[ASalbenblatt]

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• Have you added tests for any changed functionality?
• Have you added the Jira issue number
  as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
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Issue

https://otwarchive.atlassian.net/browse/AO3-5743

Purpose

This makes it so the related works count in dashboard sidebar goes down when a related work's parent is deleted so it matches the number of works shown. It also hides any sections which would look empty due to the same reason of works with deleted parents

Testing Instructions

First, create a work (the parent work) that will be listed as the inspiration for another work

1. Log in as User A
2. Post > New Work
3. Fill in required information
4. Press "Post Without Preview"
5. Note the URL of this work
6. Log out as User A

Now create a work that will cite the previous as its inspiration

1. Log in as User B
2. Post > New Work
3. Fill in required inform
4. Check "This work is a remix, a translation, a podfic, or was inspired by another work"
5. Paste the URL of the parent work in the "URL" field
6. Press "Post Without Preview"
7. Hi, username! > My Dashboard
8. Make note of how many Related Works your dashboard sidebar says you have
9. Log out

Delete the parent work

1. Log in as User A
2. Go to the work you posted
3. Edit > Delete Work
4. Confirm that you want to delete said work

Look at user B's Related Works page

1. Log in as User B
2. Dashboard > Related works
3. The count next to related work should be one lower and match the number of visible works
4. There should be no empty sections (e.g. Works that inspired User_B)

Credit

FlyingFalcon they/them