branched version can't be removed after branch removed on github

Step to reproduce:

1. Create a branch named `file-finder` and create a PR
2. PR merged
3. branch `file-finder` removed

Now, I got in packagist, branch is exists but can't be removed there:

To actually able to remove it, I need to rollback branch, and then remove it on packagist, which imo, it should be able to be removed via packagist.

I think remove branched version should be allowed like before.

Reproduce the reported flow by creating and merging a GitHub pull request from a branch, deleting the branch, and checking the corresponding Packagist version. Trace the existing branched-version removal handling and its validation. Done means a version for a deleted branch can be removed through Packagist without first restoring the branch.

Written by the indexing model from the issue text.