Issue Summary

When a Bitbucket repository is imported from a pre-Bitbucket 7.x instance to a different instance, the refs/pull-requests/* are transferred to the target instance from the source instance. The refs are packed after the Git import and end up in the $BITBUCKET_SHARED/data/repositories/<repo_id>/packed-refs. Therefore, if the source instance has open pull requests with active merge refs(refs/pull-requests/*/merge), they are transferred to the target instance and remain in the packed-refs forever, which causes them to be advertised when using the git ls-remote command.

This is reproducible on Data Center: (yes)

Steps to Reproduce

1. Create a repository on Bitbucket 6.x and make changes.
2. Create a pull request to merge the changes to another branch. This should create a merge ref under refs/pull-requests/<PR_ID>/.
3. Import the repository into a Bitbucket 7.x instance.
4. After a few minutes, a pack operation will be performed to pack all the loose refs.
5. The refs/pull-requests/* will be moved to $BITBUCKET_SHARED/data/repositories/<repo_id>/packed-refs
6. The merge refs are now packed and will never be cleaned up when a new pull request is opened on the Bitbucket 7.x instance.
7. The new pull request created on the target instance will still have an old merge ref(refs/pull-requests/*/merge attached to it that came from the source instance. However, the merge ref will be pointing to an incorrect commit ID from the source Bitbucket Instance.

Expected Results

• The refs/pull-requests/<PR_ID>/merge should be cleaned up on Bitbucket 7.x,8.x for the repository, even if it is packed and under the
  $BITBUCKET_SHARED/data/repositories/<repo_id>/packed-refs file.

Actual Results

• The merge refs are cleaned up only when a new Pull Request (on Target instance) matching the same pull request ID imported from the source instance is created, meaning when these refs are under the directory $BITBUCKET_SHARED/data/repositories/<repo_id>/refs/pull-requests/<PR_ID>/merge.
• However, if these refs are packed and moved to $BITBUCKET_SHARED/data/repositories/<repo_id>/packed-refs, they are left untouched and will be advertised forever.

Workaround

• Remove the problematic merge ref from $BITBUCKET_SHARED/data/repositories/<repo_id>/packed-refs, you need to manually delete the entry.
• Alternatively, you can remove it by running "git update-ref -d refs/pull-requests/<PR_ID>/merge" from the $BITBUCKET_SHARED/data/repositories/<repo_id> directory.