Clean up migration used for migrating merge request diff commit users
In !63669 (merged) we are adding a migration and some code changes for a new setup for storing merge request diff commit authors and committers. This merge request includes a background migration, which for GitLab.com is expected to take at least two weeks to run.
This issue is used for tracking that migration process, and setting up a new merge request to process any remaining rows, and make the new data setup the default approach.