“Prune remote branches” in Git Extensions executes git remote prune command, which removes your local remote tracking branches where the branch no longer exists on the remote.
See here: https://git-scm.com/docs/git-remote#Documentation/git-remote.txt-empruneem
Deletes stale references associated with <name>. By default, stale remote-tracking branches under <name> are deleted, but depending on global configuration and the configuration of the remote we might even prune local tags that haven’t been pushed there. Equivalent to
git fetch --prune <name>, except that no new references will be fetched.See the PRUNING section of git-fetch for what it’ll prune depending on various configuration.
With
--dry-runoption, report what branches would be pruned, but do not actually prune them.