Delete award emoji when deleting a user

## What does this MR do?

Fix the problem where a user's award emoji aren't deleted when the user is deleted.

## Are there points in the code the reviewer needs to double check?

The corresponding SELECT for the migration runs in 0.3s on staging, but I can't test the delete there or on production easily. It should be reasonably quick.

## Why was this MR needed?

There was a typo in an association 😱 

## What are the relevant issue numbers?

Closes #19693.

## Screenshots (if relevant)

Nope.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5216