The `BuildsEmailService` records were migrated to
`PipelinesEmailService` in 12dd5ac2.

That commit also deleted the corresponding spec and added a comment that
this model could be removed in 9.1.

However, there are still 305 `BuildsEmailService` records in the
GitLab.com database.

This change:

1. Deletes records in the `services` table with type of
`"BuildsEmailService"`.
2. Deletes the model

https://gitlab.com/gitlab-org/gitlab/-/issues/331064
https://gitlab.com/gitlab-org/gitlab/-/issues/332551

Changelog: removed
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63264