Fix deletion of issue assignees for MySQL
MySQL builds on EE were failing due to MySQL not liking the complex subqueries. Simplify the deletion to use a subquery that works.
For example: https://gitlab.com/gitlab-org/gitlab-ee/builds/16452985
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
MySQL builds on EE were failing due to MySQL not liking the complex subqueries. Simplify the deletion to use a subquery that works.
For example: https://gitlab.com/gitlab-org/gitlab-ee/builds/16452985