Cleanup max_hours_before_termination GraphQL field outside of deprecation milestone
MR: Pending
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## Description
Spin-off from:
gitlab-org/gitlab#509788+
Due to recent developments [preventing removal of fields](https://docs.google.com/document/d/19_7oipuumS785R6Hdsg8qLuB8qpq1lXNvGdTI1gTSYk/edit?tab=t.0) deprecated on the GraphQL layer and not marked as experimental on the breaking milestone (18.0 in this case), we need to still plan for the removal of these fields in a later milestone as they currently provide no benefit ( they are not used internally for anything)
The fields in question:
- `max_hours_before_termination` [on workspace type](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/graphql/types/remote_development/workspace_type.rb?ref_type=heads#L59) , [and mutation](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/graphql/mutations/remote_development/workspace_operations/create.rb?ref_type=heads#L30)
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## Acceptance criteria
- [ ] deprecated fields removed from GraphQL
## Implementation plan
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issue