Solve for when dag is in a versioned bundle, user tries to clear a 2.x-generated dag run

### Body After upgrade, if a dag is in a versioned bundle, the existing dag runs will not have dag versions. So, what version to use when we clear an old one? According to Jed, we should probably set the version to whatever the current version is and run with that. **I am not sure what the current behavior is.** If this is already the current behavior, just close this ticket. ### Committer - [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.