In Subversion, to cancel an svn add example_folder command before committing to the repository, do not use svn delete or svn remove or made-up stuff like undo or cancel.
Use the svn revert command:
svn revert --recursive example_folder
And all will be well.
Update: Commenter says this can lose local changes. Not sure about that, but my use case was indeed to get rid of everything so i didn't care. And i'm on Git now.
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