Remove workspace config version 1 as it is no longer needed
MR: Pending
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## Description
The following discussion from !139209 should be addressed:
- [ ] @cwoolley-gitlab started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/139209#note_1706512941): (+1 comment)
> @vtak This MR is failing on `ee/spec/lib/gitlab/background_migration/update_workspaces_config_version_spec.rb` (in [this job](https://gitlab.com/gitlab-org/gitlab/-/jobs/5814904568) due to the removal of the `VERSION_1` constant.
>
> To get this MR merged, we can just add the constant back in a new commit, then ask me to re-approve and re-merge.
>
> But I think we should eventually consider removing the spec and migration altogether.
>
> But we will need to follow the rules for that to ensure that the background migration is included in the [required upgrade path](https://docs.gitlab.com/ee/update/index.html#upgrade-paths).
>
> We should create a follow-up issue to handle that removal. I'll let you create that one.
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