Remove deprecated editor field from GraphQL API
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MR: Pending
## References
https://gitlab.com/gitlab-org/gitlab/-/issues/508155+
## Description
We need to remove references of this field in the GraphQL API ~~%"18.0"~~(no breaking changes are allowed in 18.0 milestone see [this doc](https://docs.google.com/document/d/19_7oipuumS785R6Hdsg8qLuB8qpq1lXNvGdTI1gTSYk/edit?tab=t.0)) in a future milestone, per the deprecation guidelines in https://docs.gitlab.com/ee/api/graphql/#deprecation-and-removal-process
This is a follow up to this MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/167673+ where we deprecated the `editor` field from the API in milestone %"17.5"
See details in this thread: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/167673#note_2147134342
## Acceptance Criteria
- [ ] Remove API doc references for this field
- [ ] Remove it from the create workspace mutation
- [ ] Remove it from the workspace type
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