Remove workspace config version 1 as it is no longer needed

MR: Pending

Description

The following discussion from !139209 (merged) should be addressed:

• @cwoolley-gitlab started a discussion: (+1 comment)

  @vtak This MR is failing on ee/spec/lib/gitlab/background_migration/update_workspaces_config_version_spec.rb (in this job 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.

  We should create a follow-up issue to handle that removal. I'll let you create that one.

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