Remove ai_catalog_flows feature flag from backend
What does this MR do and why?
Removes backend Ruby guards for the `ai_catalog_flows` feature flag, which has been `default_enabled: true` (beta) since milestone 18.4.
This is the backend half — merge after !239494 (merged) (frontend).
Changes:
- Delete `ee/config/feature_flags/beta/ai_catalog_flows.yml`
- Remove `flows_enabled` condition from `item_policy`, `group_policy`, `project_policy`; simplify rules to rely solely on `StageCheck flows_available`
- Remove `ai_catalog_flows_enabled?` guard from `item_consumers/create_service`
- Remove `if Feature.enabled?(:ai_catalog_flows)` conditional in search helper
- Remove disabled-flag test contexts from 3 Ruby spec files
Closes https://gitlab.com/gitlab-com/gitlab-com/-/issues/29
MR acceptance checklist
- I have evaluated the MR acceptance checklist for this MR.
Edited by Eduardo Bonet