IMHO, Git only supports "Prune obsolete worktrees" which already exists as a menu item.
But it (SmartGit) could also `rm -rf` the directory, right?
But it would be tricky, because there could be other obsolete worktrees, too, that silently could be deleted, too.
Then maybe a separate menu "Delete worktree" that only deleted the files on the disk, and then prune removes it from git?
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