<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=521995) </details> <!--IssueSummary end--> After removing the `bulk_import_importer_user_mapping` FF in https://gitlab.com/gitlab-org/gitlab/-/issues/508945, we can remove the old user mapping code from Direct Transfer. This issue is to remove the old user mapping code which is behind the code check [Import::BulkImports::EphemeralData#importer_user_mapping_enabled?](https://gitlab.com/gitlab-org/gitlab/-/blob/449f72a9666d8ccef3d84a9c618f8b3ec5d6ab65/lib/import/bulk_imports/ephemeral_data.rb#L15)