[Feature flag] Cleanup gitea_user_mapping
<!-- Title suggestion: [Feature flag] Cleanup gitea_user_mapping --> ## Summary This issue is to cleanup the `gitea_user_mapping` feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production. Since UCM will be the default, and only, approach for contribution assignment, the flag can be removed. Let's make sure to also clean up our docs, i.e., remove any mention of this flag and the deprecated user mapping approach in our docs. - https://gitlab.com/gitlab-org/gitlab/-/issues/467084 <!-- Short description of what the feature is about and link to relevant other issues. Ensure to note if the feature will be removed completely or will be productized--> **From the [refinement notes](https://gitlab.com/gitlab-org/gitlab/-/issues/520670#note_2373525132):** It's worth noting that various specs for Bitbucket Server, Gitea, and GitHub importers use the `:import_user_mapping_enabled` trait when creating a project from a factory. Once all of the old user mapping code is removed, we can remove that trait as well. Since we'll likely be cleaning up all of these flags simultaneously, it might be easier to include that as a tiny 3rd MR or make sure it's in the last open cleanup MR ## Owners - Team: Import & Integrate - Most appropriate slack channel to reach out to: `#g_import_and_integrate` - Best individual to reach out to: `@SamWord` - PM: `@m_frankiewicz` ## Stakeholders ## Expectations ### What might happen if this goes wrong? If there is an issue with this cleanup, we would need to decide whether to roll back the clean-up MR, or temporarily disable Gitea import. Individuals to contact: `@m_frankiewicz` and `@wortschi`. ### Cleaning up the feature flag <!-- The checklist here is to help stakeholders keep track of the feature flag status --> - [x] Specify in the issue description if this feature will be removed completely or will be productized as part of the Feature Flag cleanup - [ ] Create a merge request to remove `gitea_user_mapping` feature flag. Ask for review and merge it. - [ ] Remove all references to the feature flag from the codebase. - [ ] Remove the YAML definitions for the feature from the repository. - [ ] Create [a changelog entry](https://docs.gitlab.com/ee/development/feature_flags/#changelog). - [ ] Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before [the code cutoff](https://about.gitlab.com/handbook/engineering/releases/#self-managed-releases-1), the feature can be officially announced in a release blog post. - [ ] `/chatops run auto_deploy status <merge-commit-of-cleanup-mr>` - [ ] If not already done, clean up the feature flag from all environments by running these chatops command in `#production` channel: `/chatops run feature delete gitea_user_mapping --dev --pre --staging --staging-ref --production` - [ ] Close this rollout issue.
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